Comment 0 for bug 593086
Revision history for this message
| Phillip Susi (psusi) wrote Need CONFIG_LBDAF set to prevent silent wraparound on > 2 TB disks | #0 |
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bbfa235
(Get the code!)
Ubuntu kernels silently wrap access to disk locations above 2 TB back around to zero. This can easily be reproduced using lvm to create a thin provisioned virtual disk:
lvcreate --type zero -L 3t -n empty vg0
lvcreate -s -n thin vg0/zero -L 1g
mke2fs -t ext4 -E lazy_itable_init /dev/vg0/thin
e2fsck -f /dev/vg0/thin
Fsck will find errors in the bitmap because it is actually reading the superblock instead of the allocation bitmap situated just after the 2 tb mark. I emailed the dm-devel mailing list about the issue and was told that this happens when CONFIG_LBDAF is not set, and that it would be rather daft of a distribution not to set that option. I checked my config for kernel 2.6.32-22-generic on lucid amd64 and indeed, this option does not seem to be there. I also first observed this bug on i386 karmic.
I believe that this bug effects all users who have a > 2tb disk, be it virtual, physical, or raid, and can lead to unexplained loss of data. Therefore I feel it meets the criteria for a high priority bug, if not critical.