ext3 +2TB fs

[Damian Menscher]

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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