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Old 07-15-2009, 06:26 PM   #1
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Insane number of ext3 group descriptors. WTF?

I'm in the process of troubleshooting a problem where I'm not seeing a goodly chunk of my free space on an ext3 filesystem.

Some background: I had a single 500GB disk, most of which consisted of a partition containing an ext3 filesystem. In this computer, I installed a hardware RAID controller (PERC 5i) with 3 640GB disks set up in RAID5 (to Linux, it's just a ~1.2TB disk). Used dd to image the 500GB disk over to the RAID disk, used fdisk to increase the size of the main partition, and then resize2fs to expand the filesystem on that partition. Other than the time involved, no big. Problem is, 'df' (and pretty much any other filesystem tool) doesn't show any increase in the available space on the filesystem. After a bunch of poking around, the problem seems to be that half the space is taken up by group descriptors -- usually a group of 8192 blocks will have a handful of blocks used as group descriptors, but this filesystem has roughly 4000 out of the 8000 blocks in each group taken up by group descriptors. Anyone seen this one before? I'll append what I hope is useful info here:

fdisk output:

Disk /dev/sda: 1279.1 GB, 1279094947840 bytes
255 heads, 63 sectors/track, 155507 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x3f8f235b

Device Boot Start End Blocks Id System
/dev/sda1 1 63 506016 83 Linux
/dev/sda2 64 154463 1240218000 f W95 Ext'd (LBA)
/dev/sda3 154464 155507 8385930 82 Linux swap / Solaris
/dev/sda5 64 154463 1240217968+ 83 Linux

df output:

Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda5 484610513 196489383 288121130 41% /mnt/foo5

Heavily trimmed (just showing first and last group)dump2fs output:

Filesystem volume name: <none>
Last mounted on: <not available>
Filesystem UUID: 78690a12-74f4-11d3-835e-0060b0fbe51a
Filesystem magic number: 0xEF53
Filesystem revision #: 1 (dynamic)
Filesystem features: has_journal ext_attr dir_index large_file
Filesystem flags: signed_directory_hash
Default mount options: (none)
Filesystem state: clean
Errors behavior: Continue
Filesystem OS type: Linux
Inode count: 310054912
Block count: 1240217968
Reserved block count: 0
Free blocks: 288121130
Free inodes: 308919498
First block: 1
Block size: 1024
Fragment size: 1024
Blocks per group: 8192
Fragments per group: 8192
Inodes per group: 2048
Inode blocks per group: 256
Last mount time: Tue Jul 14 13:09:07 2009
Last write time: Tue Jul 14 14:46:43 2009
Mount count: 1
Maximum mount count: -1
Last checked: Mon Jul 13 16:23:46 2009
Check interval: 0 (<none>)
Reserved blocks uid: 0 (user root)
Reserved blocks gid: 0 (group root)
First inode: 11
Inode size: 128
Journal inode: 8
Default directory hash: tea
Directory Hash Seed: 99afe6ae-addf-4c04-b9ae-300ced78347a
Journal backup: inode blocks
Journal size: 32M

Group 0: (Blocks 1-8192)
Primary superblock at 1, Group descriptors at 2-4733
Block bitmap at 4734 (+4733), Inode bitmap at 4735 (+4734)
Inode table at 4736-4991 (+4735)
0 free blocks, 2031 free inodes, 4 directories
Free blocks:
Free inodes: 13, 16-21, 24-91, 93-2048

Group 151393: (Blocks 1240211457-1240217967)
Backup superblock at 1240211457, Group descriptors at 1240211458-1240216189
Block bitmap at 1240216190 (+4733), Inode bitmap at 1240216191 (+4734)
Inode table at 1240216192-1240216447 (+4735)
1520 free blocks, 2048 free inodes, 0 directories
Free blocks: 1240216448-1240217967
Free inodes: 310052865-310054912
Old 07-16-2009, 09:47 PM   #2
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The following page suggests that there was an error in your procedure.

I suspect that more google searching would be fruitful.
Old 07-16-2009, 10:41 PM   #3
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Originally Posted by stress_junkie View Post
The following page suggests that there was an error in your procedure.

I suspect that more google searching would be fruitful.
Hmmmm. Not sure where in the FM it sez that I could even potentially create a filesystem using resize2fs with group descriptors screwed up like that. Shoot, all I did (after extending the size of the partition) was a "resize2fs /dev/sda5", which tells resize2fs to expand the filesystem to fit the available space. The partition size is/was fine, and even the number of blocks in the filesystem is fine, it's just the allocation between group descriptor blocks and regular ol' usable blocks that is the issue.

I assume I'm not the first person to encounter this, but I've yet to find any solutions in Google space :-)

If I don't find a solution soon, I'll probably just have to punt and cp the contents of the partition to another filesystem, blow away the filesystem on /dev/sda5, recreate it from scratch, and cp the contents back. That'll also give me the opportunity to reset the filesystem block size to 4K instead of 1K -- you can tell this filesystem has been around since the days of dinky disks...


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