[dm-devel] 2 TB wraparound on 32 bit host

[James Bottomley]

On Fri, 2010-06-11 at 16:57 -0400, Phillip Susi wrote:
> I am seeing access to > 2tb on a dm target silently wrap around to 0.
> Simple recreation steps:
> 
> lvcreate --type zero -L 3TB -n empty vg0
> lvcreate -s vg0/empty -L 10G -n thin
> mke2fs -t ext4 -E lazy_itable_init /dev/vg0/thin
> e2fsck -f /dev/vg0/thin
> 
> The fsck will find block bitmap differences on a cleanly formatted fs
> that seem to be caused by wraparound.  Accessing block 536870912 with dd
> seems to return the superblock instead of the block allocation bitmap
> that should be located there.
> 
> This is using kernel 2.6.31-21-generic-pae i686 build from Ubuntu 9.10.
> 
> Is this a known issue and/or can anyone reproduce it?

So best guess is that CONFIG_LBDAF isn't set.  This would make all
sector_t counts wrap at 2TB (32 bits worth of 512 bytes).  It would be
rather a daft thing for a distribution not to have set, though ...

James