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Re: ext3 +2TB fs



On Fri, 25 Feb 2005, Andreas Dilger wrote:
On Feb 25, 2005  16:36 -0600, Alexander Lazarevich wrote:
> Feb 25 11:23:28 xxx kernel:  sda: sda1
> Feb 25 11:23:30 xxx kernel: SCSI device sda: 2927173632 512-byte hdwr
> sectors (1498713 MB)
> Feb 25 11:23:30 xxx kernel: SCSI device sda: drive cache: write back
> Feb 25 11:23:30 xxx kernel:  sda: sda1
> Feb 25 11:28:25 xxx kernel: EXT3-fs error (device sda1):
> ext3_check_descriptors: Inode table for group 5642 not in group (block
> 184811522)!
> Feb 25 11:28:25 xxx kernel: EXT3-fs: group descriptors corrupted !
> Feb 25 11:28:34 xxx kernel: EXT3-fs error (device sdb1):
> ext3_check_descriptors: Inode table for group 826 not in group (block
> 27000834)!
> Feb 25 11:28:34 xxx kernel: EXT3-fs: group descriptors corrupted !

The group descriptors are stored right at the start of the filesystem,
so if there is a 32-bit overflow it would corrupt them right away.

I would start by testing whether the large device works properly by
writing some pattern (e.g. 64-bit byte offset) to the start of each
4k block on disk, and then read them back to verify nothing has been
overwritten.

Out of curiosity, how would one do this? All I can think of is to script something to call dd with the seek/skip argument. But making 3.5TB/4k = a billion calls to dd out a shell seems kinda silly. What do you suggest?


Next, create directories (you may need as many as 16k) to get one that
is in the >2TB part of the disk.  You can tell by the inode number and
the output from dumpe2fs.  If you write a file in that directory it
should allocate space at > 2TB on the disk, and debugfs "stat file" will
tell you the block layout of the file.

As I understand it, the first test is to identify if the flaw exists in the kernel block-device code, and the second test whether the bug is in the ext2 code?


Anyone out there actually using a >2TB filesystem on a 32-bit machine?

Damian [works with Alex]
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