What is bit rot, and how is your favourite file system dealing with it?

redhat.com

2 points·globalc··5 comments

Can confirm that bitrot is real, especially with cheaper devices. And as far as I know, only ZFS in RAID configuration can detect and fix it today.

It’s a real pity that there is no competitors in this space. Every time I read about btrfs, I am sad that they don’t seem to consider it an important feature at all.

Of course, besides simply supporting recovery from bit rot, one would also want to have confidence in the implementation. I think the vendors which provide production support for btrfs do so just for a few features.

- XFS: can use checksummed metadata, changed data (bit rot) will not be noticed, unless extra layers like dm-integrity are used

- ext4: same as XFS

- btrfs: can with checksums detect bit rot, not heal it by itself it seems

- ceph: can detect bit rot, not repair. Ceph is for networked systems, no local file system like xfs/ext4/btrfs.

That was a fun read and I was a bit shocked that they didn't have any suggestions on remediations. Not saying they should have as the topic was bit rot not how to fix it.

I know someone who did setup ceph just for it's healing capabilities.. but of course one has to familiarize with all of it's administration aspects for that.

Setups with RAID1 could help fixing bit rot, but I think these setups are not full stack tested, so one would have to play and test by oneself (and after soft ware updates verify the whole stack again..).

Maybe easiest remedy is to keep all files in a second directory, and hope that when bit rot invalidates one version of the file the second one is ok. rsync could in cycles sync the 2 directory trees.

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