Comment by anon9001 | Hacker News Reader

Comment by anon9001 | Hacker News Reader

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Thanks for the explanation. I didn't realize md didn't use the parity checks unless there's a URE.

Is it correct to say that ZFS parity is used to reconcile on each read even without UREs, but with md parity is only used when there are UREs? If that's true, it makes much more sense why ZFS is considered the right choice.

Also, do you know if adding luks in the mix changes that?

My data goes md->lvm->luks->ext4 and I hadn't considered which part of that is supposed to catch the error if it wasn't a URE.

It makes sense that md would update parity if there was no URE. It also makes sense that LVM wouldn't know or care about data integrity.

I would think luks would require data integrity to work properly, but I'm not sure what happens if there is bitrot in a luks block.

I'm also surprised ext4 doen't have checksumming, but apparently it's only for able to checksum for metadata and it's disabled by default: https://serverfault.com/questions/456319/how-to-get-checksum...

Dm-integrity sounds worth a look, but https://raid.wiki.kernel.org/index.php/Dm-integrity doesn't inspire much confidence.

The other replies answered most of your questions so I won't retread those.

>Dm-integrity sounds worth a look, but https://raid.wiki.kernel.org/index.php/Dm-integrity doesn't inspire much confidence.

That wiki page is pretty yikes - I was under the impression dm-integrity was farther along.

Some misc other stuff I like about ZFS:

l2arc/zil on ssd/optane devices for fast read/write caching Easy NFS/SMB sharing zdb ( https://manpages.debian.org/testing/zfsutils-linux/zdb.8.en.... )

I don't think you would be disappointed if you checked it out.

I don't think ZFS checks the parity constantly, but it verifies the checksums of every block it does read.

luks won't change that at all, it'll still be at the md level overall. The main encryption modes used by luks will lose a block to bitrot and such but won't lose the rest of the drive. They essentially generate a new key (really a new IV/nonce I think?) for every block through various means. This is the only way to allow for random access to any part of the disk without having to decrypt the previous blocks, and rewriting the rest of the disk whenever you change a part in the middle. I think you can setup an authenticated luks mode, but I've not looked at it and that should catch errors but that's all it would do, catch them.

ZFS has native encryption now that is solid. So you can even avoid luks if you can live with some higher meta data leakage. There was a great talk about the details you can find on yt.

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