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by wongarsu 330 days ago
What I mean is that unraid, zfs and md all allow you to run a scrub over your raid to check for bit rot. That might happen for all kinds of issues, including cosmic rays just flipping bits on the drive platter. The issue is that unraid and md can't do much if they detect a block/stripe where the parity doesn't match the data (because it doesn't know which of the drives suffered a bit flip). Zfs on the other hand can repair the data in that scenario because it keeps checksums.

Now a fairly common scenario is to use unRaid with zfs as the file system for each partition, having Y independent zfs file systems. In that case in theory the information to repair blocks exists: a zfs scrub will tell you which blocks are bad, and you could repair those from parity. And a unraid parity check will do the same for the parity drives. But there is no system to repair single blocks. You either have to dig in and do it yourself or just resilver the whole disk
1 comments
reginald78 330 days ago
The silly part is unraid has all the pieces to do this. The btrfs file system which unraid supports for array disks could identify bitrot, and the unraid array supports virtualizing missing disks by essentially reconstructing the disk from parity and all of the other disks. Combining those two would allow rebuilding a rotted file with features already present.

My impression is unraid developers have kind of ignored enhancing the core feature of their product to much. They seem to have put a lot of effort into ZFS support which isn't that easy to integrate as it isn't part of the kernel, when ZFS isn't really the core draw of their product in the first place.

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bayindirh 329 days ago
I have driven BTRFS for test in the past.

It's too metadata heavy, and is really shines on high IOPS SSDs, it's a no go for spinning drives, esp. if they're external.

RAID5/6 is not still production ready [0], and having a non production ready feature not gated behind a "I know what I'm doing" switch is dangerous. I believe BTRFS' customers are not small fish, but enterprises which protect their data in other ways.

So, I think unraid does the right thing by not doubling down on something half-baked. ZFS is battle tested at this point.

I'm personally building a small NAS for myself and researching the software stack to use. I can't trust BTRFS with my data, esp. in RAID5/6 form, which I'm planning to do.

[0]: https://btrfs.readthedocs.io/en/latest/btrfs-man5.html#raid5...

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