[GUIDE] SD card partitioning for rooted phones

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BlaY0

Retired Recognized Developer
Sep 15, 2007
1,553
566
Medvode
Behold... a long awaited partitioning guide ;)

WARNING! This GUIDE is to actually learn something not just to copy/paste commands!

Requirements
  • rooted phone
  • busybox installed
  • parted (optional)
  • backup your SD card (optional)
  • calculator
Background

Before we begin partitioning, we need to elaborate some key points:
  1. block storage units are divided into logical blocks known as sectors
  2. sector has a size of 512 bytes
  3. NAND flash chips are divided into blocks known as erase blocks
  4. our SD cards consist of those NAND flash chips and controller
  5. erase block on our SD cards has a size of 128 kB, that's 256 sectors
  6. CHS (cylinder, head, sector) alignment has an insignificant importance here
  7. 1st sector is sector 0 (not 1) and is used as MBR (master boot record)
  8. 1st partition begins at cylinder boundary to maintain MS-DOS compatibility
  9. raw access to block storage units is done via special block device files under /dev/block directory
  10. our SD card is represented by block device file /dev/block/mmcblk0
Instructions

Here I will provide you with two methods of partitioning. For 1st method you will be using fdisk utility which is part of busybox and for 2nd a standalone utility called parted will be used. Both methods can be used in normal mode via adb shell or some terminal app. I will explain both methods using adb shell as it is more convenient and handy than typing commands via touch keyboard on your phone.

1st thing to do before you begin is to unmount your SD card via "Settings->SD & phone storage" and then you issue "adb shell" command ony your PC. 2nd thing you will do is erasing of your SD card (actually you will erase just first few erase blocks of your SD card) using dd utility:
Code:
dd if=/dev/zero of=/dev/block/mmcblk0 bs=131072 count=16
...that will overwrite 1st 2 MB of your SD card with null characters. Next you may begin with partitioning.
fdisk
As I already stated, fdisk is a (interactive) utility that is part of busybox so I will assume it is available under /system/xbin directory. Now you can run fdisk with device file of your SD card as parameter/argument:
Code:
fdisk /dev/block/mmcblk0
...this will bring you some notes on your screen you should not worry about and a command prompt:
Code:
Command (m for help):
...which you can leave at any time by pressing CTRL+C. Next you will change unit display type to sectors:
Code:
Command (m for help): [B]u[/B]
Changing display/entry units to sectors
...and print your SD's current info (this is info of my SD card actually, yours may vary):
Code:
Command (m for help): [B]p[/B]

Disk /dev/block/mmcblk0: 8018 MB, 8018460672 bytes
4 heads, 16 sectors/track, 244704 cylinders, total 15661056 sectors
Units = sectors of 1 * 512 = 512 bytes

              Device Boot      Start         End      Blocks  Id System
...and you write down the number of sectors. In my case it is 15661056 sectors of 512 bytes which is exactly 7647 MB if we divide them by 2048. For example you would take 7000 MB for fat32 1st partition and 647 MB for ext 2nd partition. and it is handy that way coz megabytes are divisible by our SD card's erase block size which is 128 kB as stated before. Calculation would give you start sector for 2nd partition and this would be 14336000 (7000*2048).

Now you need to create 2 primary partitions:
Code:
Command (m for help): [B]n[/B]
Command action
   e   extended
   p   primary partition (1-4)
[B]p[/B]
Partition number (1-4): [B]1[/B]
...now there's a catch. You will be offeread a start of 1st partition at 1st to 2nd cylinder boundary which is sector 16 in my case and you push it to SD card's erase block boundary (256):
Code:
First sector (16-15661055, default 16): [B]256[/B]
Last sector or +size or +sizeM or +sizeK (256-15661055, default 15661055): [B]14335999[/B]
...and continue to the next partition which should also be primary:
Code:
Command (m for help): [B]n[/B]
Command action
   e   extended
   p   primary partition (1-4)
[B]p[/B]
Partition number (1-4): [B]2[/B]
First sector (16-15661055, default 16): [B]14336000[/B]
Last sector or +size or +sizeM or +sizeK (14336000-15661055, default 15661055): [B]15661055[/B]
...now print what you have just done:
Code:
Command (m for help): [B]p[/B]

Disk /dev/block/mmcblk0: 8018 MB, 8018460672 bytes
4 heads, 16 sectors/track, 244704 cylinders, total 15661056 sectors
Units = sectors of 1 * 512 = 512 bytes

              Device Boot      Start         End      Blocks  Id System
/dev/block/mmcblk0p1             256    14335999     7167872  83 Linux
/dev/block/mmcblk0p2        14336000    15661055      662528  83 Linux
...it looks OK but you need to change 1st partition's hex id which needs to be fat32 (c):
Code:
Command (m for help): [B]t[/B]
Partition number (1-4): [B]1[/B]
Hex code (type L to list codes): [B]c[/B]
Changed system type of partition 1 to c (Win95 FAT32 (LBA))
...now you're am set, print again your configuration and write changes to SD card:
Code:
Command (m for help): [B]p[/B]

Disk /dev/block/mmcblk0: 8018 MB, 8018460672 bytes
4 heads, 16 sectors/track, 244704 cylinders, total 15661056 sectors
Units = sectors of 1 * 512 = 512 bytes

              Device Boot      Start         End      Blocks  Id System
/dev/block/mmcblk0p1             256    14335999     7167872   c Win95 FAT32 (LBA)
/dev/block/mmcblk0p2        14336000    15661055      662528  83 Linux

Command (m for help): [B]w[/B]
The partition table has been altered!
There's a possibility you would need to shutdown and power on again your phone at this point. Do not reboot via adb or some 3rd party app!
parted
Parted is one of interactive partitioning utilities that can also use external formatting utilities. It can be found in some recovery images but can be copied to your internal phone storage and run from there in normal mode too. To run it you have to use your SD card's device file as a parameter/argument:
Code:
parted /dev/block/mmcblk0
...and you will be presented with an interactive shell:
Code:
GNU Parted 1.8.8.1.179-aef3
Using /dev/block/mmcblk0
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted)
I probably shouldn't mention that there's an interactive help available and that it is invoked by issuing "help" into shell's command prompt. Next thing to do is making a MS-DOS disklabel:
Code:
(parted) [B]mklabel msdos[/B]
...and switch to display sector as a unit:
Code:
(parted) [B]unit s[/B]
Now you can print some useful info:
Code:
(parted) [B]print all[/B]
Model: SD USD (sd/mmc)
Disk /dev/block/mmcblk0: 15661056s
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start      End        Size       Type     File system  Flags
Mind and write down the size in sectors (15661056 in my case).If you divide number of sectors by 2048, you get how big in MB is actually your SD card (7647 in my case).You should mind that erase block of your SD card is 128 kB and all of your partitions should start at the beginnings of those erase blocks. It is safe to say that 1st partition should begin at sector 256 and 2nd at any MB boundary. Let say you want 512 MB big ext partition and the rest for fat32 one. Mind tho that 1st partition is to be fat32! So we say 7135 MB for fat32 1st partition and 512 MB for ext 2nd partition. Now you calculate the start sector of 2nd partition... number of MB for 1st partition multiplied by 2048 should give you the number (14612480). And you are set for partitioning:
Code:
(parted) [B]mkpart primary fat32 256 14612479[/B]
(parted) [B]mkpart primary ext2 14612480 15661055[/B]
...and print result:
Code:
(parted) [B]print all[/B]
Model: SD USD (sd/mmc)
Disk /dev/block/mmcblk0: 15661056s
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start      End        Size       Type     File system  Flags
 1      256s       14612479s  14612224s  primary  fat32        lba
 2      14612480s  15661055s  1048576s   primary  ext2
...and quit:
Code:
(parted) [B]quit[/B]
At this point you have partitioned your SD card but not yet formatted it. Format fat32 partition with mkfs.vfat and ext partition with mkfs.ext2:
Code:
mkfs.vfat /dev/block/mmcblk0p1
...and:
Code:
mkfs.ext2 -m0 -b4096 /dev/block/mmcblk0p2
If there is a mke2fs utility on your phone system (standalone - not part of busybox), you may use it to format second partition as ext3:
Code:
mke2fs -j -m0 -b4096 /dev/block/mmcblk0p2
...or even as ext4 (if your mke2fs supports that):
Code:
mke2fs -j -m0 -b4096  -Oextents,uninit_bg,dir_index /dev/block/mmcblk0p2
 
Last edited:

Learners Lisence

Senior Member
Jun 28, 2010
187
4
Blayo,

thanks for the post. You always manage to take things to an entirely different level of understanding :)

Is this guide for the successful implementation of the latest data2ext scripts in roms ? in comparison to methods like the Rom Manager and partition through recovery ?
 

Dr.Romca

Senior Member
Dec 12, 2008
768
207
Prague
No, it is general guide to better understand partitioning etc.
I totally agree! After going through parted I think it's the best way to partition your SD, you have complete control!
I can't wait will my new SD card arrives, and give this a shot!
The Kingston 16GB class 10 sucks even when set-up to the best parameters and the reason for that is simple: Although class 10, it is like 4 times slower than my 8GD sandisk mobile ultra Class 4 when random writing and 3 times slower when reading...
So Thanks BlaY0 for this cool guide/lesson ;)
 

tasar

Senior Member
Mar 17, 2007
712
127
I have problem with fdisk . when i press p i got this info and there a no sector:

PHP:
Command (m for help): p
p

Disk /dev/block/mmcblk0: 16.0 GB, 16001269760
4 heads, 16 sectors/track, 488320 cylinders
Units = cylinders of 64 * 512 = 32768 bytes
 

tasar

Senior Member
Mar 17, 2007
712
127
Thanks, with the "u" option comes later in your manual ;)
A last newbie question: i have now 2 part. and formated the FAT, but i dont know, how to get the "mke2fs" on the phone to format the Linux part.?
Sorry Blay0 but Linux is another Word for me...
 

BlaY0

Retired Recognized Developer
Sep 15, 2007
1,553
566
Medvode
Thanks, with the "u" option comes later in your manual ;)
Thanx, I have changed that.
A last newbie question: i have now 2 part. and formated the FAT, but i dont know, how to get the "mke2fs" on the phone to format the Linux part.?
Sorry Blay0 but Linux is another Word for me...
If you have busybox on your phone you also have mke2fs or mkfs.ext2 as these two are part of it. If you have CM based ROM there should already be standalone e2fsprogs in /system/bin directory and if you have a stock based one, you can find mke2fs_recvy + e2fsck_recvy in /system/bin directory. In B ROM you have all e2fsprogs available in /system/xbin directory.
 
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curto

Senior Member
Aug 7, 2010
144
10
Sydney
Code:
# mkfs.vfat /dev/block/mmcblk0p1
mkfs.vfat /dev/block/mmcblk0p1
mkfs.vfat: not found

help? :confused:
 

curto

Senior Member
Aug 7, 2010
144
10
Sydney
Try "busybox mkfs.vfat"...

Code:
# busybox mkfs.vfat /dev/block/mmcblk0p1
busybox mkfs.vfat /dev/block/mmcblk0p1
mkfs.vfat: applet not found

its ok, before you replied i tried doing it in recovery and i believe it worked, but i think i missed a digit in my partitioning and it was only 98mb for my fat drive instead of about 988 or something (1gb) so ill try it again and let you know

EDIT: ok yeah i had the digits wrong so now its formatted/partitioned correctly. now im gonna apply the data2ext thing and see what happens. i didnt actually do anything about my darktremor a2sd so ive probably got bits and pieces of all my apps missing but if **** starts to screw up ill just put a fresh copy of cm on since ive ruined all my apps basically already

EDIT: alright its working, thanks heaps!
 
Last edited:

BlaY0

Retired Recognized Developer
Sep 15, 2007
1,553
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Medvode
DT has some commands to disable itself.

As for mkfs.vfat... it is part of busybox but not necesarily. There are several versions lying around the internets. Type just "busybox" and you'll see all the utils available in it.
 

curto

Senior Member
Aug 7, 2010
144
10
Sydney
DT has some commands to disable itself.

As for mkfs.vfat... it is part of busybox but not necesarily. There are several versions lying around the internets. Type just "busybox" and you'll see all the utils available in it.

Code:
# busybox
busybox
BusyBox v1.16.2androidfull (2010-08-01 14:57:25 EDT) multi-call binary.
Copyright (C) 1998-2009 Erik Andersen, Rob Landley, Denys Vlasenko
and others. Licensed under GPLv2.
See source distribution for full notice.

Usage: busybox [function] [arguments]...
   or: function [arguments]...

        BusyBox is a multi-call binary that combines many common Unix
        utilities into a single executable.  Most people will create a
        link to busybox for each function they wish to use and BusyBox
        will act like whatever it was invoked as.

Currently defined functions:
        [, [[, arp, ash, awk, basename, bbconfig, brctl, bunzip2, bzcat, bzip2,
        cal, cat, catv, chgrp, chmod, chown, chroot, cksum, clear, cmp, cp,
        cpio, cut, date, dc, dd, depmod, devmem, df, diff, dirname, dmesg,
        dnsd, dos2unix, du, echo, ed, egrep, env, expr, false, fdisk, fgrep,
        find, fold, free, freeramdisk, fuser, getopt, grep, gunzip, gzip, head,
        hexdump, id, ifconfig, insmod, install, ip, kill, killall, killall5,
        length, less, ln, losetup, ls, lsmod, lspci, lsusb, lzop, lzopcat,
        md5sum, mkdir, mke2fs, mkfifo, mkfs.ext2, mknod, mkswap, mktemp,
        modprobe, more, mount, mountpoint, mv, nc, netstat, nice, nohup,
        nslookup, ntpd, od, patch, pgrep, pidof, ping, pkill, printenv, printf,
        ps, pwd, rdev, readlink, realpath, renice, reset, rm, rmdir, rmmod,
        route, run-parts, sed, seq, setsid, sh, sha1sum, sha256sum, sha512sum,
        sleep, sort, split, stat, strings, stty, swapoff, swapon, sync, sysctl,
        tac, tail, tar, tee, telnet, test, tftp, time, top, touch, tr,
        traceroute, true, tty, tune2fs, umount, uname, uniq, unix2dos, unlzop,
        unzip, uptime, usleep, uudecode, uuencode, vi, watch, wc, wget, which,
        whoami, xargs, yes, zcat

yeah so that mkfs.vfat isnt there and neither is parted
and then when i go to android recovery

Code:
# busybox
busybox
BusyBox v1.15.3 (2010-02-06 17:13:19 CET) multi-call binary
Copyright (C) 1998-2008 Erik Andersen, Rob Landley, Denys Vlasenko
and others. Licensed under GPLv2.
See source distribution for full notice.

Usage: busybox [function] [arguments]...
   or: function [arguments]...

        BusyBox is a multi-call binary that combines many common Unix
        utilities into a single executable.  Most people will create a
        link to busybox for each function they wish to use and BusyBox
        will act like whatever it was invoked as!

Currently defined functions:
        [, [[, arping, ash, awk, basename, bbconfig, bunzip2, bzcat, bzip2,
        cat, catv, chattr, chgrp, chmod, chown, chroot, chrt, chvt, cksum,
        clear, cmp, cp, crond, crontab, cut, date, dc, dd, deallocvt, depmod,
        devmem, df, dhcprelay, diff, dirname, dmesg, dnsd, dnsdomainname,
        dos2unix, du, dumpkmap, dumpleases, echo, egrep, env, ether-wake, expr,
        false, fbset, fbsplash, fdisk, fgrep, find, fold, free, freeramdisk,
        fsck, fuser, getopt, grep, gunzip, gzip, head, hexdump, hostname,
        hwclock, ifconfig, ifdown, ifup, insmod, install, ip, ipaddr, ipcalc,
        iplink, iproute, iprule, iptunnel, kbd_mode, kill, killall, killall5,
        last, length, less, ln, loadfont, loadkmap, losetup, ls, lsattr, lsmod,
        makedevs, md5sum, mdev, mkdir, mkdosfs, mkfifo, mkfs.vfat, mknod,
        mkswap, mktemp, modprobe, more, mount, mountpoint, mv, nameif, nc,
        netstat, nice, nmeter, nohup, nslookup, od, openvt, patch, pidof, ping,
        pipe_progress, pivot_root, printenv, printf, ps, pscan, pwd, rdate,
        rdev, readlink, readprofile, realpath, renice, reset, resize, rm,
        rmdir, rmmod, route, run-parts, sed, seq, setconsole, setkeycodes,
        setlogcons, setsid, sh, sha1sum, showkey, sleep, sort, split, stat,
        strings, stty, sum, swapoff, swapon, switch_root, sync, sysctl, tac,
        tail, tar, tcpsvd, tee, telnet, telnetd, test, tftp, time, top, touch,
        tr, traceroute, true, tty, tunctl, udhcpd, udpsvd, umount, uname,
        uncompress, uniq, unix2dos, unzip, uptime, usleep, uudecode, uuencode,
        vconfig, vi, watch, wc, wget, which, who, whoami, xargs, yes, zcat

and boom, a lot more stuff is there (except parted.. but it works anyways, and mkfs.ext2 is missing, and doesnt work). it should be okay to do everything in recovery anyways right? and i can just use mke2fs -m0 -b4096 /dev/block/mmcblk0p2 to format the ext2 partition?

EDIT: just tried the parted method and i dont think it works, i get this

Code:
(parted) mkpart primary fat32 256 2813951
mkpart primary fat32 256 2813951
mkpart primary fat32 256 2813951
(parted) mkpart primary ext2 2813952 3862527
mkpart primary ext2 2813952 3862527
mkpart primary ext2 2813952 3862527
(parted) print all
print all
print all
Model: SD SU02G (sd/mmc)
Disk /dev/block/mmcblk0: 3862528s
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start     End       Size      Type     File system  Flags
 1      256s      2813951s  2813696s  primary               lba
 2      2813952s  3862527s  1048576s  primary

anyways i used the first method and its fine, although the partitioning isnt spot on accurate, i just put on data2ext for cm6 and my available space is 504mb instead of 512mb and i checked all my calculations and everything, ah well close enough. thanks again!
 
Last edited:

playahate

Senior Member
Oct 7, 2010
142
90
42
Moscow
Need some help.
There's a possibility you would need to shutdown and power on again your phone at this point.
Possibility?
I got this:
Code:
Command (m for help): p
p

Disk /dev/block/mmcblk0: 7973 MB, 7973371904 bytes
4 heads, 16 sectors/track, 243328 cylinders, total 15572992 sectors
Units = sectors of 1 * 512 = 512 bytes

              Device Boot      Start         End      Blocks  Id System
/dev/block/mmcblk0p1             256    13475839     6737792   c Win95 FAT32 (LBA)
/dev/block/mmcblk0p2        13475840    15572991     1048576  83 Linux
Then i got
Code:
Command (m for help): mkfs.vfat /dev/block/mmcblk0p1
mkfs.vfat /dev/block/mmcblk0p1
Command Action
a       toggle a bootable flag
b       edit bsd disklabel
c       toggle the dos compatibility flag
d       delete a partition
l       list known partition types
n       add a new partition
o       create a new empty DOS partition table
p       print the partition table
q       quit without saving changes
s       create a new empty Sun disklabel
t       change a partition's system id
u       change display/entry units
v       verify the partition table
w       write table to disk and exit
x       extra functionality (experts only)
The same with the mkfs.ext2 -m0 -b4096 /dev/block/mmcblk0p2
And now the phone says than my flash is empty or uses wrong format, dont want to mount it and want to format it. I press cancel.
if i make p again it shows:
Code:
Command (m for help): p
p

Disk /dev/block/mmcblk0: 7973 MB, 7973371904 bytes
4 heads, 16 sectors/track, 243328 cylinders
Units = cylinders of 64 * 512 = 32768 bytes

              Device Boot      Start         End      Blocks  Id System
What is my mistake?

UPD: Seems like it worked with the parted
Code:
C:\androidsdk\platform-tools>adb shell
adb server is out of date.  killing...
* daemon started successfully *
# dd if=/dev/zero of=/dev/block/mmcblk0 bs=131072 count=16
dd if=/dev/zero of=/dev/block/mmcblk0 bs=131072 count=16
16+0 records in
16+0 records out
2097152 bytes transferred in 0.568 secs (3692169 bytes/sec)
# parted /dev/block/mmcblk0
parted /dev/block/mmcblk0
GNU Parted 1.8.8.1.179-aef3
Using /dev/block/mmcblk0
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) mklabel msdos
mklabel msdos
mklabel msdos
(parted) unit s
unit s
unit s
(parted) print all
print all
print all
Model: SD SA08G (sd/mmc)
Disk /dev/block/mmcblk0: 15572992s
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start  End  Size  Type  File system  Flags


(parted) mkpart primary fat32 256 13475839
mkpart primary fat32 256 13475839
mkpart primary fat32 256 13475839
(parted) mkpart primary ext2 13475840 15572992
mkpart primary ext2 13475840 15572992
mkpart primary ext2 13475840 15572992
Error: The location 15572992 is outside of the device /dev/block/mmcblk0.
(parted) mkpart primary ext2 13475840 15572991
mkpart primary ext2 13475840 15572991
mkpart primary ext2 13475840 15572991
(parted) print all
print all
print all
Model: SD SA08G (sd/mmc)
Disk /dev/block/mmcblk0: 15572992s
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start      End        Size       Type     File system  Flags
 1      256s       13475839s  13475584s  primary               lba
 2      13475840s  15572991s  2097152s   primary


(parted) quit
quit
quit
Information: You may need to update /etc/fstab.

# mkfs.vfat /dev/block/mmcblk0p1
mkfs.vfat /dev/block/mmcblk0p1
# mkfs.ext2 -m0 -b4096 /dev/block/mmcblk0p2
mkfs.ext2 -m0 -b4096 /dev/block/mmcblk0p2
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
65536 inodes, 262144 blocks
0 blocks (0%) reserved for the super user
First data block=0
Maximum filesystem blocks=4194304
8 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376
 
Last edited:

BlaY0

Retired Recognized Developer
Sep 15, 2007
1,553
566
Medvode
Absolutely. You neet to write the partition table exiting fdisk. And you can't execute mkfs.vfat and mke2fs inside fdisk shell! It's the same as you would try to microwave your sandwich in the fridge... it won't work that way...
 
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playahate

Senior Member
Oct 7, 2010
142
90
42
Moscow
agrrrrr. didnt see the next line with the w.
anyway i made it by parted. very good guide, very good rom =)
lil question: can i make ext3 or ext4 at any time? (after using data2ext).will it work correctly or wipe all data? or just when i make partitionong?
 

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  • 33
    Behold... a long awaited partitioning guide ;)

    WARNING! This GUIDE is to actually learn something not just to copy/paste commands!

    Requirements
    • rooted phone
    • busybox installed
    • parted (optional)
    • backup your SD card (optional)
    • calculator
    Background

    Before we begin partitioning, we need to elaborate some key points:
    1. block storage units are divided into logical blocks known as sectors
    2. sector has a size of 512 bytes
    3. NAND flash chips are divided into blocks known as erase blocks
    4. our SD cards consist of those NAND flash chips and controller
    5. erase block on our SD cards has a size of 128 kB, that's 256 sectors
    6. CHS (cylinder, head, sector) alignment has an insignificant importance here
    7. 1st sector is sector 0 (not 1) and is used as MBR (master boot record)
    8. 1st partition begins at cylinder boundary to maintain MS-DOS compatibility
    9. raw access to block storage units is done via special block device files under /dev/block directory
    10. our SD card is represented by block device file /dev/block/mmcblk0
    Instructions

    Here I will provide you with two methods of partitioning. For 1st method you will be using fdisk utility which is part of busybox and for 2nd a standalone utility called parted will be used. Both methods can be used in normal mode via adb shell or some terminal app. I will explain both methods using adb shell as it is more convenient and handy than typing commands via touch keyboard on your phone.

    1st thing to do before you begin is to unmount your SD card via "Settings->SD & phone storage" and then you issue "adb shell" command ony your PC. 2nd thing you will do is erasing of your SD card (actually you will erase just first few erase blocks of your SD card) using dd utility:
    Code:
    dd if=/dev/zero of=/dev/block/mmcblk0 bs=131072 count=16
    ...that will overwrite 1st 2 MB of your SD card with null characters. Next you may begin with partitioning.
    fdisk
    As I already stated, fdisk is a (interactive) utility that is part of busybox so I will assume it is available under /system/xbin directory. Now you can run fdisk with device file of your SD card as parameter/argument:
    Code:
    fdisk /dev/block/mmcblk0
    ...this will bring you some notes on your screen you should not worry about and a command prompt:
    Code:
    Command (m for help):
    ...which you can leave at any time by pressing CTRL+C. Next you will change unit display type to sectors:
    Code:
    Command (m for help): [B]u[/B]
    Changing display/entry units to sectors
    ...and print your SD's current info (this is info of my SD card actually, yours may vary):
    Code:
    Command (m for help): [B]p[/B]
    
    Disk /dev/block/mmcblk0: 8018 MB, 8018460672 bytes
    4 heads, 16 sectors/track, 244704 cylinders, total 15661056 sectors
    Units = sectors of 1 * 512 = 512 bytes
    
                  Device Boot      Start         End      Blocks  Id System
    ...and you write down the number of sectors. In my case it is 15661056 sectors of 512 bytes which is exactly 7647 MB if we divide them by 2048. For example you would take 7000 MB for fat32 1st partition and 647 MB for ext 2nd partition. and it is handy that way coz megabytes are divisible by our SD card's erase block size which is 128 kB as stated before. Calculation would give you start sector for 2nd partition and this would be 14336000 (7000*2048).

    Now you need to create 2 primary partitions:
    Code:
    Command (m for help): [B]n[/B]
    Command action
       e   extended
       p   primary partition (1-4)
    [B]p[/B]
    Partition number (1-4): [B]1[/B]
    ...now there's a catch. You will be offeread a start of 1st partition at 1st to 2nd cylinder boundary which is sector 16 in my case and you push it to SD card's erase block boundary (256):
    Code:
    First sector (16-15661055, default 16): [B]256[/B]
    Last sector or +size or +sizeM or +sizeK (256-15661055, default 15661055): [B]14335999[/B]
    ...and continue to the next partition which should also be primary:
    Code:
    Command (m for help): [B]n[/B]
    Command action
       e   extended
       p   primary partition (1-4)
    [B]p[/B]
    Partition number (1-4): [B]2[/B]
    First sector (16-15661055, default 16): [B]14336000[/B]
    Last sector or +size or +sizeM or +sizeK (14336000-15661055, default 15661055): [B]15661055[/B]
    ...now print what you have just done:
    Code:
    Command (m for help): [B]p[/B]
    
    Disk /dev/block/mmcblk0: 8018 MB, 8018460672 bytes
    4 heads, 16 sectors/track, 244704 cylinders, total 15661056 sectors
    Units = sectors of 1 * 512 = 512 bytes
    
                  Device Boot      Start         End      Blocks  Id System
    /dev/block/mmcblk0p1             256    14335999     7167872  83 Linux
    /dev/block/mmcblk0p2        14336000    15661055      662528  83 Linux
    ...it looks OK but you need to change 1st partition's hex id which needs to be fat32 (c):
    Code:
    Command (m for help): [B]t[/B]
    Partition number (1-4): [B]1[/B]
    Hex code (type L to list codes): [B]c[/B]
    Changed system type of partition 1 to c (Win95 FAT32 (LBA))
    ...now you're am set, print again your configuration and write changes to SD card:
    Code:
    Command (m for help): [B]p[/B]
    
    Disk /dev/block/mmcblk0: 8018 MB, 8018460672 bytes
    4 heads, 16 sectors/track, 244704 cylinders, total 15661056 sectors
    Units = sectors of 1 * 512 = 512 bytes
    
                  Device Boot      Start         End      Blocks  Id System
    /dev/block/mmcblk0p1             256    14335999     7167872   c Win95 FAT32 (LBA)
    /dev/block/mmcblk0p2        14336000    15661055      662528  83 Linux
    
    Command (m for help): [B]w[/B]
    The partition table has been altered!
    There's a possibility you would need to shutdown and power on again your phone at this point. Do not reboot via adb or some 3rd party app!
    parted
    Parted is one of interactive partitioning utilities that can also use external formatting utilities. It can be found in some recovery images but can be copied to your internal phone storage and run from there in normal mode too. To run it you have to use your SD card's device file as a parameter/argument:
    Code:
    parted /dev/block/mmcblk0
    ...and you will be presented with an interactive shell:
    Code:
    GNU Parted 1.8.8.1.179-aef3
    Using /dev/block/mmcblk0
    Welcome to GNU Parted! Type 'help' to view a list of commands.
    (parted)
    I probably shouldn't mention that there's an interactive help available and that it is invoked by issuing "help" into shell's command prompt. Next thing to do is making a MS-DOS disklabel:
    Code:
    (parted) [B]mklabel msdos[/B]
    ...and switch to display sector as a unit:
    Code:
    (parted) [B]unit s[/B]
    Now you can print some useful info:
    Code:
    (parted) [B]print all[/B]
    Model: SD USD (sd/mmc)
    Disk /dev/block/mmcblk0: 15661056s
    Sector size (logical/physical): 512B/512B
    Partition Table: msdos
    
    Number  Start      End        Size       Type     File system  Flags
    Mind and write down the size in sectors (15661056 in my case).If you divide number of sectors by 2048, you get how big in MB is actually your SD card (7647 in my case).You should mind that erase block of your SD card is 128 kB and all of your partitions should start at the beginnings of those erase blocks. It is safe to say that 1st partition should begin at sector 256 and 2nd at any MB boundary. Let say you want 512 MB big ext partition and the rest for fat32 one. Mind tho that 1st partition is to be fat32! So we say 7135 MB for fat32 1st partition and 512 MB for ext 2nd partition. Now you calculate the start sector of 2nd partition... number of MB for 1st partition multiplied by 2048 should give you the number (14612480). And you are set for partitioning:
    Code:
    (parted) [B]mkpart primary fat32 256 14612479[/B]
    (parted) [B]mkpart primary ext2 14612480 15661055[/B]
    ...and print result:
    Code:
    (parted) [B]print all[/B]
    Model: SD USD (sd/mmc)
    Disk /dev/block/mmcblk0: 15661056s
    Sector size (logical/physical): 512B/512B
    Partition Table: msdos
    
    Number  Start      End        Size       Type     File system  Flags
     1      256s       14612479s  14612224s  primary  fat32        lba
     2      14612480s  15661055s  1048576s   primary  ext2
    ...and quit:
    Code:
    (parted) [B]quit[/B]
    At this point you have partitioned your SD card but not yet formatted it. Format fat32 partition with mkfs.vfat and ext partition with mkfs.ext2:
    Code:
    mkfs.vfat /dev/block/mmcblk0p1
    ...and:
    Code:
    mkfs.ext2 -m0 -b4096 /dev/block/mmcblk0p2
    If there is a mke2fs utility on your phone system (standalone - not part of busybox), you may use it to format second partition as ext3:
    Code:
    mke2fs -j -m0 -b4096 /dev/block/mmcblk0p2
    ...or even as ext4 (if your mke2fs supports that):
    Code:
    mke2fs -j -m0 -b4096  -Oextents,uninit_bg,dir_index /dev/block/mmcblk0p2
    1
    Did you change units display to sectors?
    1
    Thanks, with the "u" option comes later in your manual ;)
    Thanx, I have changed that.
    A last newbie question: i have now 2 part. and formated the FAT, but i dont know, how to get the "mke2fs" on the phone to format the Linux part.?
    Sorry Blay0 but Linux is another Word for me...
    If you have busybox on your phone you also have mke2fs or mkfs.ext2 as these two are part of it. If you have CM based ROM there should already be standalone e2fsprogs in /system/bin directory and if you have a stock based one, you can find mke2fs_recvy + e2fsck_recvy in /system/bin directory. In B ROM you have all e2fsprogs available in /system/xbin directory.
    1
    Need some help.
    Code:
    Command (m for help): p
    p
    
    Disk /dev/block/mmcblk0: 7973 MB, 7973371904 bytes
    4 heads, 16 sectors/track, 243328 cylinders
    Units = cylinders of 64 * 512 = 32768 bytes
    
                  Device Boot      Start         End      Blocks  Id System
    What is my mistake?

    I got this too... seems I forgot to enter the "w" command to write the partitions. :p
    1
    Absolutely. You neet to write the partition table exiting fdisk. And you can't execute mkfs.vfat and mke2fs inside fdisk shell! It's the same as you would try to microwave your sandwich in the fridge... it won't work that way...