26 Sep 09 Shrinking/Resizing ext3 Partitions

Shrinking or expanding an ext3 partition is easy but is not without it’s risks. Before starting, you NEED to take a backup of your data. There’s a strong possibility that it will all disappear and your filesystem will become permenantly broken, as with any disk or filesystem procedure.

Please note:

1. The steps below are the RAW STEPS required to resize your partition. This is a potentially dangerous procedure that could easily destroy/ruin/damage your partition, data, filesystem or other partitions on the same disk.
2. DO NOT perform these steps on a live/production machine
3. DO NOT perform these steps unless you have a full backup of your data/disk
4. These steps are really for theoretical purposes only. They should work just fine, but tools such as gparted will do this for you.

ns3:~# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1             9.4G  6.8G  2.2G  77% /
tmpfs                 443M     0  443M   0% /lib/init/rw
udev                   10M   92K   10M   1% /dev
tmpfs                 443M     0  443M   0% /dev/shm
/dev/sdb1              20G  9.8G  9.0G  52% /email

In my example, I’m going to resize /dev/sdb1 which is my /email partition. /dev/sdb1 is a partition residing on device /dev/sdb

At this point, we need to look at our filesystem in terms of 4K block size:

ns3:~# df -B 4k
Filesystem           4K-blocks      Used Available Use% Mounted on
/dev/sda1              2458888   1775171    558813  77% /
tmpfs                   113165         0    113165   0% /lib/init/rw
udev                      2560        23      2537   1% /dev
tmpfs                   113165         0    113165   0% /dev/shm
/dev/sdb1              5158933   2544177   2352696  52% /email

Now you’ll need to know the size of /dev/sdb1:

ns3:~# fdisk -s /dev/sdb1
20964824

Now before you go ahead, you’ll need to reboot and boot up from a Linux CD that contains support for your hardware and root filesystem, as well as tools such as fdisk, fsck, tune2fs and resize2fs.

Firstly, make sure your filesystem hasn’t been automatically mounted: umount /dev/sdb1

You also need to make sure that your filesystem is clean: fsck -n /dev/sdb1

Now assuming everything so far has been successful, it’s time to begin. Even though resize2fs supports ext3 filesystems, I recommend converting your filesystem to ext2 first: tune2fs -O ^has_journal /dev/sdb1

Now, e2fsck -f /dev/sdb1

At this point, you’ll have a clean ext2 filesystem. I’ll now resize my filesystem to 12GB: resize2fs /dev/sdb1 12G

The output is:

resize2fs 1.38 (30-Jun-2005)
Resizing the filesystem on /dev/sda1 to 3145728 (4k) blocks.
The filesystem on /dev/sda1 is now 3145728 blocks long.

This number has been calculated as follows: 12GB * 1024 = 12,288MB. 12288MB * 1024 = 12,582,912KB.
12582914KB = 3145728 4K blocks.

Now we’ll use fdisk to delete and recreate the partition.

fdisk /dev/sdb

First enter d then enter 1. This will DELETE your sdb1 partition. This is OK, as we’re not actually deleting any data itself, just the partition metadata. Now we’ll need to create a new partition. To do so, enter n then enter p to specify that we’re creating a primary partition, then 1 to specify partition number 1.

When asked for the first cylinder, enter ‘1′. When asked Last cylinder or +size or +sizeM or +sizeK (1-1247, default 1247): We want the value that we calculated above in KB. I would also add 3% to be safe, although I’m confident that this isn’t strictly necessary: 12,582,912KB * 1.03 = 12,960,399.36. So we’ll enter +12960400K

If we want this to be a bootable partition, we would then enter a then 1. Finally enter p to print the proposed table and confirm that everything is as we want it, then finally w to write.

I’d recommend a reboot, followed by a fsck -n /dev/sdb1

Now we’ll add the journal again, tune2fs -j /dev/sdb1 and finally remount our partition mount /dev/sdb1 /mnt/disk confirming that our size change has been successful with df

Tags: df, ext3, fdisk, fsck, resize, resize2fs, tune2fs

Leave a Comment