Speaking of Raid 5

Michael Torrie torriem at chem.byu.edu
Fri Nov 24 20:32:37 MST 2006

On Fri, 2006-11-24 at 20:15 -0700, Sterling Jacobson wrote:
> I just had TWO of the four hard drives in my Raid 5 array die today!
> Now I need some help figuring out how to get my data back since I wasn't exactly counting on a double failure.
> One of the SCSI drives sounds like two stones rubbing each other at 10k RPM. 
> The other just says "Media Error" from my Adaptec BIOS init.
> Any ideas?

A two disk-failure is catastrophic, sorry.  If the data is valuable, you
can pay much money to a data recovery center.  There is no way to
recover your data otherwise that I know of, unless you can by some
miracle get one of the two failed disks to work long enough to get your
data off.

The double-disk failure really is an Achilles heal for RAID-5.  I'm
installing a new disk array at work that is 10 raw terabytes.  I'll be
making it a RAID-6 (which is really RAID-5 but with two parity stripes
instead of one), which should help mitigate this.  There's no substitute
for a backup, though!

RAID-10 give the best odds, as the odds of losing any two-disk
combination that leads to a failure is quite low.

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