Using ZFS as RAID0 - disk offline question

[Ivan Voras]

On 04/06/2012 22:38, Matthew Seaman wrote:

> No.  A RAID0 zpool will be marked offline if any of the drives within it
> fails.  You might be able to recover some data from remaining drives,
> but not easily.  The surest way of getting anything back would be to go
> to a specialist disaster recovery company, but expect to pay $$$ for it.
>  Considering the price of hard drives nowadays, this would be a dumb
> choice: you could easily convert your RAID0 to a RAID10 for much less
> than it would cost you to try and recover from a broken RAID0.
> 
> Even if you do install a replacement disk, ZFS won't be able to rebuild
> from your original drive.  You'ld have to wipe and rebuild from scratch.

This requires a more thorough answer from someone who's working on ZFS
or has done extensive testing, but there is a particular circumstance in
which (in theory), ZFS could recover from RAID0 failure: if the "ditto
blocks" feature is turned on.

E.g.:  https://blogs.oracle.com/relling/entry/zfs_copies_and_data_protection

I think this would only work if the second drive isn't disconnected but
continues to respond with IO errors while reading. If the drive is
disconnected, the whole array will probably fail.

Ditto blocks sort-of-but-not-quite turn ZFS RAID0 into RAID-10.

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