[GUIDE] Introduction to the OnePlus 8T - Why is it so?

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BillGoss

Senior Member
Sep 2, 2010
5,157
4,524
Sydney
OnePlus 3T
What it ain't: it's not a "how-to" manual. There are lots of threads out there that explain how to do things.

What it is: a fairly simple explanation of how things are on this phone written for for those who, like me, have come from a phone with no A/B partitions (a far simpler world).

"Toto, I've a feeling we're not in Kansas anymore"​

The OnePlus 8T is an AB device. This means that a large number (but not all) of its hardware partitions have an A and a B version. The A set of partitions are called slot a, the B set are slot b.
The reason for this is to support seamless over-the-air (OTA) updates. These are updates to the operating system (OS) that can be installed while the phone is being used! Once the update has been installed the phone is rebooted (it automatically switches slots) and comes up on the newly updated version of the OS. If the update fails, the phone will simply revert to the original slot.

To implement this a number of things have changed:
  1. The AB partitions have a currently active/running version (called the active slot) and an inactive version (the inactive slot) where the updates can be written to.
  2. An update module (update_engine) is included in the OS to process the updates. Previously this would have been handled by code running in the recovery partition.
  3. To avoid doubling up on large system partitions (system, system_ext, odm, product, vendor) and to can cater for increases in these partions, these are now carved out dynamically from a large super partition. This allows more effective use of the hardware space.

This has some important implications:
  • While it looks like you could have two versions of the operating system installed on the phone (one on slot a, one on slot b), this is not in fact the case. And that's because the super partition isn't large enough to hold two sets of system partitions. Just like there's only one version of the data partition, so there's only one version of the super partition (containing the system partitions).
  • You can write to hardware partitions in bootloader/fastboot mode using fastboot flash <partition> <file>, but you can't use this mode to write a specific file within a partition. And, therefore, you can't use this mode to write to the system partitions because they are files within the super partition. For these, you need to use fastbootd which is part of recovery.
  • Flashing/installing a ROM using the update engine (as done by System update of OOS or a recovery from LineageOS or TWRP) will always be written to the inactive slot. So, if you are flashing a custom ROM and want it to use the latest OOS firmware installed on the phone, then you will have to either:
    1. Copy the firmware from the currently active slot to the inactive one, or
    2. Swap slots before you do the install so that it gets installed on what was the active slot containing the correct firmware.
  • If you are used to using TWRP to backup your system partitions, then the way to do it now is to backup the super partition and not the system, system_ext, odm, product, or vendor partitions.

    "It's complicated"​

    "Delta variants"​

    Updates (whether Over-the-air (OTA) or from the OnePlus download site) come in two flavours:
    1. Full update: the files for each updated partition contain the full image. These are quite large, typically about 2.8GB.
    2. Delta update: the files contain only the changes to be applied to each partition and can be quite small in size (MB rather than GB).
    Since a delta update only contains changes, it is imperative that the update process check that the current partition contains the expected data that will be updated. The update_engine will check that the current partition hash is what the update is expecting. If it isn't, the update will fail.
    If a partition has been modified (you have installed Magisk which changes the boot partition, or installed TWRP which changes the recovery partition), then you will have to restore the changed partition back to their original stock version before starting the update process.
    That's why it is best practice to take a copy of the stock partition before you modify it.

    "Good memories"​

    The 8T came out originally with LPDDR4X memory, but OnePlus then decided to improve it by using LPDDR5 memory. As a result of this change, the xbl and xbl_config partitions now hold different data depending on the type of memory used in the phone. Note: you can find out what type of memory your phone has using getprop ro.boot.ddr_type - 0 means LPDDR4X, 1 means LPDDR5.
    The way this is implemented is by including files for both LPDDR4X (files named xbl, xbl_config) and LPDDR5 (files named xbl_lp5, xbl_config_lp5) in updates/downloads. OnePlus had to make custom changes to update_engine to cater for this. It is only as of 2021-12-22 that a version of TWRP was produced that could handle these files correctly.

    "Hitting the books"​

    Google has some great documentation about AB devices. If you are using your phone to read this, make sure you use your browser in desktop mode so that you can see the Google documentation's navigation pane on the left hand side.
    A/B (Seamless) System Updates: https://source.android.com/devices/tech/ota/ab
    Dynamic Partitions: https://source.android.com/devices/tech/ota/dynamic_partitions
    Fastbootd: https://source.android.com/devices/tech/ota/dynamic_partitions/implement#fastbootd and https://source.android.com/devices/bootloader/fastbootd
    Virtual A/B Overview: this covers how the system partitions in super get updated and it's fairly complex https://source.android.com/devices/tech/ota/virtual_ab
 
Last edited:

zzjea

Senior Member
Thanks Bill. Very helpful and that is why I'm still on OOS for now. I'm sure I am missing something but I have several questions.
1. How is the 8T different from the 8 or 8Pro as far as OOS is concerned? Is it a different OS architecture?
2. When you use another OS like LineageOS, how does it compare to OOS as far as the internals go (super partition, etc.). Is the OS completely different in the way it uses the hardware and the way updates occur?
3. When we refer to firmware what do we actually mean (code designed exactly for the specific harware interface or what)? Does the firmware stay the same for any OS that is used and if so how is that accomplished? Are there certain areas of the system that are not touched by any new OS for that phone except the OEM?

I'm trying to wrap my head around how this phone seems to be so different from even other OP phones.
Thanks John
 
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Qnorsten

Senior Member
Mar 14, 2012
226
113
Thanks Bill. Very helpful and that is why I'm still on OOS for now. I'm sure I am missing something but I have several questions.
1. How is the 8T different from the 8 or 8Pro as far as OOS is concerned? Is it a different OS architecture?
2. When you use another OS like LineageOS, how does it compare to OOS as far as the internals go (super partition, etc.). Is the OS completely different in the way it uses the hardware and the way updates occur?
3. When we refer to firmware what do we actually mean (code designed exactly for the specific harware interface or what)? Does the firmware stay the same for any OS that is used and if so how is that accomplished? Are there certain areas of the system that are not touched by any new OS for that phone except the OEM?

I'm trying to wrap my head around how this phone seems to be so different from even other OP phones.
Thanks John
I am not Bill, but I will still attempt to answer your questions.

1. There are no real difference between OOS for 8T compared to the 8/8 Pro. They all use the same SOC (Snapdragon 865). For the last few OOS updates the changelog has been the same between 8/8Pro and 8T. Only thing that is different compared to the 8/8Pro is that the 8T device can have either LPDDR4X or LPDDR5 ram. While the 8 and 8 Pro only have either of them depending on the model. There are also plenty of unified custom kernels that work for all 3 devices as well.

2. I am no custom rom expert but I think they still handle the super partition and updates in the same way, but it is best to check the thread for the rom and read the update instructions there.

3. The FAQ in this thread should answer your questions. It also contain flashable firmware packages. These packages are extracted from the stock OOS rom and can be used to update firmware if you are on a custom rom https://forum.xda-developers.com/t/firmware-oneplus-8t-kebab-ddr0-ddr1-updated.4299231/
 

BillGoss

Senior Member
Sep 2, 2010
5,157
4,524
Sydney
OnePlus 3T
Thanks Bill. Very helpful and that is why I'm still on OOS for now. I'm sure I am missing something but I have several questions.
1. How is the 8T different from the 8 or 8Pro as far as OOS is concerned? Is it a different OS architecture?
2. When you use another OS like LineageOS, how does it compare to OOS as far as the internals go (super partition, etc.). Is the OS completely different in the way it uses the hardware and the way updates occur?
3. When we refer to firmware what do we actually mean (code designed exactly for the specific harware interface or what)? Does the firmware stay the same for any OS that is used and if so how is that accomplished? Are there certain areas of the system that are not touched by any new OS for that phone except the OEM?

I'm trying to wrap my head around how this phone seems to be so different from even other OP phones.
Thanks John
1. I don't know anything about the other OP 8 devices. I'm only interested in the 8T because that's what I have.
2. The hardware determines how the OS must be structured. So all ROMs have to support the A/B structure and dynamic system partitions.
3. I think of Firmware as phone specific software/data related to the underlying vendor-specific hardware components/chip set. It's required by the OS to access the hardware, but is not included in custom ROMs. It's vendor-specific.
 
Last edited:

nadnan

Member
Feb 20, 2018
39
13
What it ain't: it's not a "how-to" manual. There are lots of threads out there that explain how to do things.

What it is: a fairly simple explanation of how things are on this phone written for for those who, like me, have come from a phone with no A/B partitions (a far simpler world).

"Toto, I've a feeling we're not in Kansas anymore"​

The OnePlus 8T is an AB device. This means that a large number (but not all) of its hardware partitions have an A and a B version. The A set of partitions are called slot a, the B set are slot b.
The reason for this is to support seamless over-the-air (OTA) updates. These are updates to the operating system (OS) that can be installed while the phone is being used! Once the update has been installed the phone is rebooted (it automatically switches slots) and comes up on the newly updated version of the OS. If the update fails, the phone will simply revert to the original slot.

To implement this a number of things have changed:
  1. The AB partitions have a currently active/running version (called the active slot) and an inactive version (the inactive slot) where the updates can be written to.
  2. An update module (update_engine) is included in the OS to process the updates. Previously this would have been handled by code running in the recovery partition.
  3. To avoid doubling up on large system partitions (system, system_ext, odm, product, vendor) and to can cater for increases in these partions, these are now carved out dynamically from a large super partition. This allows more effective use of the hardware space.

This has some important implications:
  • While it looks like you could have two versions of the operating system installed on the phone (one on slot a, one on slot b), this is not in fact the case. And that's because the super partition isn't large enough to hold two sets of system partitions. Just like there's only one version of the data partition, so there's only one version of the super partition (containing the system partitions).
  • You can write to hardware partitions in bootloader/fastboot mode using fastboot flash <partition> <file>, but you can't use this mode to write a specific file within a partition. And, therefore, you can't use this mode to write to the system partitions because they are files within the super partition. For these, you need to use fastbootd which is part of recovery.
  • Flashing/installing a ROM using the update engine (as done by System update of OOS or a recovery from LineageOS or TWRP) will alwaysbe written to the inactive slot. So, if you are flashing a custom ROM and want it to use the latest OOS firmware installed on the phone, then you will have to either:
    1. Copy the firmware from the currently active slot to the inactive one, or
    2. Swap slots before you do the install so that it gets installed on what was the active slot containing the correct firmware.
  • If you are used to using TWRP to backup your system partitions, then the way to do it now is to backup the super partition and not the system, system_ext, odm, product, or vendor partitions.

    "It's complicated"​

    "Delta variants"​

    Updates (whether Over-the-air (OTA) or from the OnePlus download site) come in two flavours:
    1. Full update: the files for each updated partition contain the full image. These are quite large, typically about 2.8GB.
    2. Delta update: the files contain only the changes to be applied to each partition and can be quite small in size (MB rather than GB).
    Since a delta update only contains changes, it is imperative that the update process check that the current partition contains the expected data that will be updated. The update_engine will check that the current partition hash is what the update is expecting. If it isn't, the update will fail.
    If a partition has been modified (you have installed Magisk which changes the boot partition, or installed TWRP which changes the recovery partition), then you will have to restore the changed partition back to their original stock version before starting the update process.
    That's why it is best practice to take a copy of the stock partition before you modify it.

    "Good memories"​

    The 8T came out originally with LPDDR4X memory, but OnePlus then decided to improve it by using LPDDR5 memory. As a result of this change, the xbl and xbl_config partitions now hold different data depending on the type of memory used in the phone. Note: you can find out what type of memory your phone has using getprop ro.boot.ddr_type - 0 means LPDDR4X, 1 means LPDDR5.
    The way this is implemented is by including files for both LPDDR4X (files named xbl, xbl_config) and LPDDR5 (files named xbl_lp5, xbl_config_lp5) in updates/downloads. OnePlus had to make custom changes to update_engine to cater for this. It is only as of 2021-12-22 that a version of TWRP was produced that could handle these files correctly.

    "Hitting the books"​

    Google has some great documentation about AB devices. If you are using your phone to read this, make sure you use your browser in desktop mode so that you can see the Google documentation's navigation pane on the left hand side.
    A/B (Seamless) System Updates: https://source.android.com/devices/tech/ota/ab
    Dynamic Partitions: https://source.android.com/devices/tech/ota/dynamic_partitions
    Fastbootd: https://source.android.com/devices/tech/ota/dynamic_partitions/implement#fastbootd and https://source.android.com/devices/bootloader/fastbootd
    Virtual A/B Overview: this covers how the system partitions in super get updated and it's fairly complex https://source.android.com/devices/tech/ota/virtual_ab
Device OnePlus 8 Pro
OOS 11.0.10.10 IN11BA
TWRP 3.6
Root Magisk 23.0
Hello
Hello
I noted in your information above
“If you are used to using TWRP to backup your system partitions, then the way to do it now is to backup the super partition and not the system, system_ext, odm, product, or vendor partitions. »
It is precisely the use of TWRP that I took to back up my old LG or Samsung devices (S7, EDG or Tab 4 tablet)
Before the appearance of "dynamic partitions", there were no questions to ask to make a "Nandroid Backup" of your smartphone.
Now, since the arrival of OOS 10 and 11, things are different.
So here is my question for you:
If I check all the boxes by doing the backup and restore with TWRP (version 3.6.0), will the smartphone return to its general and precise state at the time of the backup? (See attached screenshots from TWRP)
If I understood correctly, TWRP performs a global image (super partition including A and B ) of all partitions at the time of backup, similar to an image of an SSD or HDD with several partitions… That's good that ?
I thank you in advance for your information and explanations and your instructions so that I can perform a "Nandroid Backup" and a possible restoration in complete safety.
Best regards
Jean-Noel
 

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BillGoss

Senior Member
Sep 2, 2010
5,157
4,524
Sydney
OnePlus 3T
Device OnePlus 8 Pro
OOS 11.0.10.10 IN11BA
TWRP 3.6
Root Magisk 23.0
Hello
Hello
I noted in your information above
“If you are used to using TWRP to backup your system partitions, then the way to do it now is to backup the super partition and not the system, system_ext, odm, product, or vendor partitions. »
It is precisely the use of TWRP that I took to back up my old LG or Samsung devices (S7, EDG or Tab 4 tablet)
Before the appearance of "dynamic partitions", there were no questions to ask to make a "Nandroid Backup" of your smartphone.
Now, since the arrival of OOS 10 and 11, things are different.
So here is my question for you:
If I check all the boxes by doing the backup and restore with TWRP (version 3.6.0), will the smartphone return to its general and precise state at the time of the backup? (See attached screenshots from TWRP)
If I understood correctly, TWRP performs a global image (super partition including A and B ) of all partitions at the time of backup, similar to an image of an SSD or HDD with several partitions… That's good that ?
I thank you in advance for your information and explanations and your instructions so that I can perform a "Nandroid Backup" and a possible restoration in complete safety.
Best regards
Jean-Noel
TWRP does image backups generally, but does file-based backups for data and some others (if I remember correctly, persist and EFS).
The "system" partitions on the OP8T are, as I mentioned, boot, dtbo, and super. This means that a "full" backup like in the "old days" is data plus the "system" partitions.

You could backup the other items in the TWRP backup list, but I'm going to ask you: Why do you want you do that?
 

nadnan

Member
Feb 20, 2018
39
13
TWRP does image backups generally, but does file-based backups for data and some others (if I remember correctly, persist and EFS).
The "system" partitions on the OP8T are, as I mentioned, boot, dtbo, and super. This means that a "full" backup like in the "old days" is data plus the "system" partitions.

You could backup the other items in the TWRP backup list, but I'm going to ask you: Why do you want you do that?
Hello
Thank you for your feedback.
I have taken note of the three system partitions you indicate.
With devices without a dynamic partition, I was "used" to saving all the data "as a precaution" on an external memory card and I was not limited in storage.
On the OnePlus 8 Pro, I have 256 GB of storage (without an external SD Card) and I could effectively limit the backup to the “Boot”, “DTBO” and “Super (System Syystem_ext product vendor)” partitions that you specify.
But I think that if I want to protect myself from any malfunction of the device after the restoration, it is better that I select all the partitions and then copy to PC the whole TWRP folder created by the " Nandroid”.
I could also buy a USB C / OTG adapter / SD card reader to store the backup…
Do you think I'm wrong?
Thanks again for your advice….
Best regards,
 

BillGoss

Senior Member
Sep 2, 2010
5,157
4,524
Sydney
OnePlus 3T
Hello
Thank you for your feedback.
I have taken note of the three system partitions you indicate.
With devices without a dynamic partition, I was "used" to saving all the data "as a precaution" on an external memory card and I was not limited in storage.
On the OnePlus 8 Pro, I have 256 GB of storage (without an external SD Card) and I could effectively limit the backup to the “Boot”, “DTBO” and “Super (System Syystem_ext product vendor)” partitions that you specify.
But I think that if I want to protect myself from any malfunction of the device after the restoration, it is better that I select all the partitions and then copy to PC the whole TWRP folder created by the " Nandroid”.
I could also buy a USB C / OTG adapter / SD card reader to store the backup…
Do you think I'm wrong?
Thanks again for your advice….
Best regards,
Backing up partitions that you don't understand how they are used is rather pointless in my mind.
Restoring a partition that you don't understand how it's used is asking for trouble.
So I would never do that. But this is your phone and you can do whatever you want with it. Though learning more about how your device works and how the various partitions are used is a really good idea.

PS: you say you have an 8 Pro. You do realise that this is an 8T forum and that I'm writing about the 8T, not any other phone?
 

nadnan

Member
Feb 20, 2018
39
13
Backing up partitions that you don't understand how they are used is rather pointless in my mind.
Restoring a partition that you don't understand how it's used is asking for trouble.
So I would never do that. But this is your phone and you can do whatever you want with it. Though learning more about how your device works and how the various partitions are used is a really good idea.

PS: you say you have an 8 Pro. You do realise that this is an 8T forum and that I'm writing about the 8T, not any other phone?
Thank you for your remarks
Yes, I know about the 8T forum but I got here while researching the web and read that the OOS build is the same for both devices...
On the other hand, I have retained your words to know what each partition was used for and I will also direct my research on this subject.
Thanks again for your availability...
Sincerely...
 

Klusio19

Senior Member
Nov 13, 2018
95
12
OnePlus 8T
Very intersting topic, and great explenation so far. I've came from old-school smartphone (Pocophone F1, without A/B partitions) and everything was so simple back then... I was about to switch from ROM to ROM on my brand new OP 8T , but I came into your topic and I realised that's something different. I have to search for some more info, because I'm looking forward to switch to colorOS (Or just other ROM in general. I just like switching and modifying my phone xD), but I'm wondering if, and how can I restore everything to stock, will I loose some widevine, mobile payment etc. I think everything is possible, I just have to make proper research. Anyway thank you again for that very interesting article!
 
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    What it ain't: it's not a "how-to" manual. There are lots of threads out there that explain how to do things.

    What it is: a fairly simple explanation of how things are on this phone written for for those who, like me, have come from a phone with no A/B partitions (a far simpler world).

    "Toto, I've a feeling we're not in Kansas anymore"​

    The OnePlus 8T is an AB device. This means that a large number (but not all) of its hardware partitions have an A and a B version. The A set of partitions are called slot a, the B set are slot b.
    The reason for this is to support seamless over-the-air (OTA) updates. These are updates to the operating system (OS) that can be installed while the phone is being used! Once the update has been installed the phone is rebooted (it automatically switches slots) and comes up on the newly updated version of the OS. If the update fails, the phone will simply revert to the original slot.

    To implement this a number of things have changed:
    1. The AB partitions have a currently active/running version (called the active slot) and an inactive version (the inactive slot) where the updates can be written to.
    2. An update module (update_engine) is included in the OS to process the updates. Previously this would have been handled by code running in the recovery partition.
    3. To avoid doubling up on large system partitions (system, system_ext, odm, product, vendor) and to can cater for increases in these partions, these are now carved out dynamically from a large super partition. This allows more effective use of the hardware space.

    This has some important implications:
    • While it looks like you could have two versions of the operating system installed on the phone (one on slot a, one on slot b), this is not in fact the case. And that's because the super partition isn't large enough to hold two sets of system partitions. Just like there's only one version of the data partition, so there's only one version of the super partition (containing the system partitions).
    • You can write to hardware partitions in bootloader/fastboot mode using fastboot flash <partition> <file>, but you can't use this mode to write a specific file within a partition. And, therefore, you can't use this mode to write to the system partitions because they are files within the super partition. For these, you need to use fastbootd which is part of recovery.
    • Flashing/installing a ROM using the update engine (as done by System update of OOS or a recovery from LineageOS or TWRP) will always be written to the inactive slot. So, if you are flashing a custom ROM and want it to use the latest OOS firmware installed on the phone, then you will have to either:
      1. Copy the firmware from the currently active slot to the inactive one, or
      2. Swap slots before you do the install so that it gets installed on what was the active slot containing the correct firmware.
    • If you are used to using TWRP to backup your system partitions, then the way to do it now is to backup the super partition and not the system, system_ext, odm, product, or vendor partitions.

      "It's complicated"​

      "Delta variants"​

      Updates (whether Over-the-air (OTA) or from the OnePlus download site) come in two flavours:
      1. Full update: the files for each updated partition contain the full image. These are quite large, typically about 2.8GB.
      2. Delta update: the files contain only the changes to be applied to each partition and can be quite small in size (MB rather than GB).
      Since a delta update only contains changes, it is imperative that the update process check that the current partition contains the expected data that will be updated. The update_engine will check that the current partition hash is what the update is expecting. If it isn't, the update will fail.
      If a partition has been modified (you have installed Magisk which changes the boot partition, or installed TWRP which changes the recovery partition), then you will have to restore the changed partition back to their original stock version before starting the update process.
      That's why it is best practice to take a copy of the stock partition before you modify it.

      "Good memories"​

      The 8T came out originally with LPDDR4X memory, but OnePlus then decided to improve it by using LPDDR5 memory. As a result of this change, the xbl and xbl_config partitions now hold different data depending on the type of memory used in the phone. Note: you can find out what type of memory your phone has using getprop ro.boot.ddr_type - 0 means LPDDR4X, 1 means LPDDR5.
      The way this is implemented is by including files for both LPDDR4X (files named xbl, xbl_config) and LPDDR5 (files named xbl_lp5, xbl_config_lp5) in updates/downloads. OnePlus had to make custom changes to update_engine to cater for this. It is only as of 2021-12-22 that a version of TWRP was produced that could handle these files correctly.

      "Hitting the books"​

      Google has some great documentation about AB devices. If you are using your phone to read this, make sure you use your browser in desktop mode so that you can see the Google documentation's navigation pane on the left hand side.
      A/B (Seamless) System Updates: https://source.android.com/devices/tech/ota/ab
      Dynamic Partitions: https://source.android.com/devices/tech/ota/dynamic_partitions
      Fastbootd: https://source.android.com/devices/tech/ota/dynamic_partitions/implement#fastbootd and https://source.android.com/devices/bootloader/fastbootd
      Virtual A/B Overview: this covers how the system partitions in super get updated and it's fairly complex https://source.android.com/devices/tech/ota/virtual_ab
    2
    Thanks Bill. Very helpful and that is why I'm still on OOS for now. I'm sure I am missing something but I have several questions.
    1. How is the 8T different from the 8 or 8Pro as far as OOS is concerned? Is it a different OS architecture?
    2. When you use another OS like LineageOS, how does it compare to OOS as far as the internals go (super partition, etc.). Is the OS completely different in the way it uses the hardware and the way updates occur?
    3. When we refer to firmware what do we actually mean (code designed exactly for the specific harware interface or what)? Does the firmware stay the same for any OS that is used and if so how is that accomplished? Are there certain areas of the system that are not touched by any new OS for that phone except the OEM?

    I'm trying to wrap my head around how this phone seems to be so different from even other OP phones.
    Thanks John
    I am not Bill, but I will still attempt to answer your questions.

    1. There are no real difference between OOS for 8T compared to the 8/8 Pro. They all use the same SOC (Snapdragon 865). For the last few OOS updates the changelog has been the same between 8/8Pro and 8T. Only thing that is different compared to the 8/8Pro is that the 8T device can have either LPDDR4X or LPDDR5 ram. While the 8 and 8 Pro only have either of them depending on the model. There are also plenty of unified custom kernels that work for all 3 devices as well.

    2. I am no custom rom expert but I think they still handle the super partition and updates in the same way, but it is best to check the thread for the rom and read the update instructions there.

    3. The FAQ in this thread should answer your questions. It also contain flashable firmware packages. These packages are extracted from the stock OOS rom and can be used to update firmware if you are on a custom rom https://forum.xda-developers.com/t/firmware-oneplus-8t-kebab-ddr0-ddr1-updated.4299231/
    2
    Backing up partitions that you don't understand how they are used is rather pointless in my mind.
    Restoring a partition that you don't understand how it's used is asking for trouble.
    So I would never do that. But this is your phone and you can do whatever you want with it. Though learning more about how your device works and how the various partitions are used is a really good idea.

    PS: you say you have an 8 Pro. You do realise that this is an 8T forum and that I'm writing about the 8T, not any other phone?
    Thank you for your remarks
    Yes, I know about the 8T forum but I got here while researching the web and read that the OOS build is the same for both devices...
    On the other hand, I have retained your words to know what each partition was used for and I will also direct my research on this subject.
    Thanks again for your availability...
    Sincerely...
    1
    Thanks Bill. Very helpful and that is why I'm still on OOS for now. I'm sure I am missing something but I have several questions.
    1. How is the 8T different from the 8 or 8Pro as far as OOS is concerned? Is it a different OS architecture?
    2. When you use another OS like LineageOS, how does it compare to OOS as far as the internals go (super partition, etc.). Is the OS completely different in the way it uses the hardware and the way updates occur?
    3. When we refer to firmware what do we actually mean (code designed exactly for the specific harware interface or what)? Does the firmware stay the same for any OS that is used and if so how is that accomplished? Are there certain areas of the system that are not touched by any new OS for that phone except the OEM?

    I'm trying to wrap my head around how this phone seems to be so different from even other OP phones.
    Thanks John
    1
    What it ain't: it's not a "how-to" manual. There are lots of threads out there that explain how to do things.

    What it is: a fairly simple explanation of how things are on this phone written for for those who, like me, have come from a phone with no A/B partitions (a far simpler world).

    "Toto, I've a feeling we're not in Kansas anymore"​

    The OnePlus 8T is an AB device. This means that a large number (but not all) of its hardware partitions have an A and a B version. The A set of partitions are called slot a, the B set are slot b.
    The reason for this is to support seamless over-the-air (OTA) updates. These are updates to the operating system (OS) that can be installed while the phone is being used! Once the update has been installed the phone is rebooted (it automatically switches slots) and comes up on the newly updated version of the OS. If the update fails, the phone will simply revert to the original slot.

    To implement this a number of things have changed:
    1. The AB partitions have a currently active/running version (called the active slot) and an inactive version (the inactive slot) where the updates can be written to.
    2. An update module (update_engine) is included in the OS to process the updates. Previously this would have been handled by code running in the recovery partition.
    3. To avoid doubling up on large system partitions (system, system_ext, odm, product, vendor) and to can cater for increases in these partions, these are now carved out dynamically from a large super partition. This allows more effective use of the hardware space.

    This has some important implications:
    • While it looks like you could have two versions of the operating system installed on the phone (one on slot a, one on slot b), this is not in fact the case. And that's because the super partition isn't large enough to hold two sets of system partitions. Just like there's only one version of the data partition, so there's only one version of the super partition (containing the system partitions).
    • You can write to hardware partitions in bootloader/fastboot mode using fastboot flash <partition> <file>, but you can't use this mode to write a specific file within a partition. And, therefore, you can't use this mode to write to the system partitions because they are files within the super partition. For these, you need to use fastbootd which is part of recovery.
    • Flashing/installing a ROM using the update engine (as done by System update of OOS or a recovery from LineageOS or TWRP) will alwaysbe written to the inactive slot. So, if you are flashing a custom ROM and want it to use the latest OOS firmware installed on the phone, then you will have to either:
      1. Copy the firmware from the currently active slot to the inactive one, or
      2. Swap slots before you do the install so that it gets installed on what was the active slot containing the correct firmware.
    • If you are used to using TWRP to backup your system partitions, then the way to do it now is to backup the super partition and not the system, system_ext, odm, product, or vendor partitions.

      "It's complicated"​

      "Delta variants"​

      Updates (whether Over-the-air (OTA) or from the OnePlus download site) come in two flavours:
      1. Full update: the files for each updated partition contain the full image. These are quite large, typically about 2.8GB.
      2. Delta update: the files contain only the changes to be applied to each partition and can be quite small in size (MB rather than GB).
      Since a delta update only contains changes, it is imperative that the update process check that the current partition contains the expected data that will be updated. The update_engine will check that the current partition hash is what the update is expecting. If it isn't, the update will fail.
      If a partition has been modified (you have installed Magisk which changes the boot partition, or installed TWRP which changes the recovery partition), then you will have to restore the changed partition back to their original stock version before starting the update process.
      That's why it is best practice to take a copy of the stock partition before you modify it.

      "Good memories"​

      The 8T came out originally with LPDDR4X memory, but OnePlus then decided to improve it by using LPDDR5 memory. As a result of this change, the xbl and xbl_config partitions now hold different data depending on the type of memory used in the phone. Note: you can find out what type of memory your phone has using getprop ro.boot.ddr_type - 0 means LPDDR4X, 1 means LPDDR5.
      The way this is implemented is by including files for both LPDDR4X (files named xbl, xbl_config) and LPDDR5 (files named xbl_lp5, xbl_config_lp5) in updates/downloads. OnePlus had to make custom changes to update_engine to cater for this. It is only as of 2021-12-22 that a version of TWRP was produced that could handle these files correctly.

      "Hitting the books"​

      Google has some great documentation about AB devices. If you are using your phone to read this, make sure you use your browser in desktop mode so that you can see the Google documentation's navigation pane on the left hand side.
      A/B (Seamless) System Updates: https://source.android.com/devices/tech/ota/ab
      Dynamic Partitions: https://source.android.com/devices/tech/ota/dynamic_partitions
      Fastbootd: https://source.android.com/devices/tech/ota/dynamic_partitions/implement#fastbootd and https://source.android.com/devices/bootloader/fastbootd
      Virtual A/B Overview: this covers how the system partitions in super get updated and it's fairly complex https://source.android.com/devices/tech/ota/virtual_ab
    Device OnePlus 8 Pro
    OOS 11.0.10.10 IN11BA
    TWRP 3.6
    Root Magisk 23.0
    Hello
    Hello
    I noted in your information above
    “If you are used to using TWRP to backup your system partitions, then the way to do it now is to backup the super partition and not the system, system_ext, odm, product, or vendor partitions. »
    It is precisely the use of TWRP that I took to back up my old LG or Samsung devices (S7, EDG or Tab 4 tablet)
    Before the appearance of "dynamic partitions", there were no questions to ask to make a "Nandroid Backup" of your smartphone.
    Now, since the arrival of OOS 10 and 11, things are different.
    So here is my question for you:
    If I check all the boxes by doing the backup and restore with TWRP (version 3.6.0), will the smartphone return to its general and precise state at the time of the backup? (See attached screenshots from TWRP)
    If I understood correctly, TWRP performs a global image (super partition including A and B ) of all partitions at the time of backup, similar to an image of an SSD or HDD with several partitions… That's good that ?
    I thank you in advance for your information and explanations and your instructions so that I can perform a "Nandroid Backup" and a possible restoration in complete safety.
    Best regards
    Jean-Noel