On 21/12/17 23:14, Lew Wolfgang wrote:
On 12/21/2017 03:07 PM, Wols Lists wrote:
On 21/12/17 22:55, Lew Wolfgang wrote:
On 12/21/2017 01:22 PM, Wols Lists wrote:
If you've got raid-6 you can recover from
corruption/failure - just make sure you run regular scrubs to detect
One tiny correction: with RAID-6 you can recover from any two failed
disks. RAID-5 allows
recovery from any single-disk failure.
Yes but :-)
Raid 5 will not let you recover from corruption. Raid 6 will, but only
one disk ...
Please explain, you lost me there.
Raid 5 has one parity disk. It will therefore let you reconstruct one
piece of missing information. If you know disk 2 has failed, you can
reconstruct the contents.
Raid 6 has TWO parity disks, so you can reconstruct TWO pieces of
missing information. If you know disks 2 and 5 have failed you can
reconstruct them both.
But if you know ONE drive (but you don't know which one) has had a
hiccup and corrupted your data - maybe a write got lost, maybe (and this
apparently does happen) the drive firmware wrote a block in the wrong
place, you can also reconstruct that! You can work out which drive has
been corrupted (the first piece of missing information) and what the
data should have been (the second piece of missing information).
There's a program (raid6check, iirc) which will recover that for you.
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