Reminder -- RAID 5 is not your friend

[blu-Z8efaSeK1ezqlBn2x/YWAg at public.gmane.org (Edward Ned Harvey)]

Surely you must have known when you built something raid-5 or raidz, that
you are taking a calculated risk of 2 disks failing at the same time, right?
Just as you now know you're risking your OS on a mirror, right?  And you are
again risking your data pool on raid-10.

Incidentally, a 2-disk failure would also kill raidz.

Everything is a calculated risk.  Use raid5 or raidz when you want.  This is
reduced risk compared to non-redundant disks.  It reduces your risk further
if you have a hotspare.  It reduces your risk further if you have raidz2 or
raid6.  It reduces your risk further if you mirror the whole setup.  It
reduces further if you get redundant raid controllers on separate buses.
And further reduced with redundant systems in an automatic failover mode.

Everything is a calculated risk.  Choose raid5 or any other level of
redundancy to suit your needs.



> -----Original Message-----
> From: discuss-bounces-mNDKBlG2WHs at public.gmane.org [mailto:discuss-bounces-mNDKBlG2WHs at public.gmane.org] On
> Behalf Of Dan Ritter
> Sent: Wednesday, March 10, 2010 11:28 PM
> To: discuss-mNDKBlG2WHs at public.gmane.org
> Subject: Reminder -- RAID 5 is not your friend
> 
> RAID 5 is not your friend.
> 
> (RAID 6 may be your friend. RAID Z may be your friend. This is
> not about those.)
> 
> A server with a mirrored setup for system disks and a RAID 5 for
> storage reported a disk gone bad in the storage system. OK, the
> alert is received, and we plan to replace the disk in the
> morning.
> 
> Before we can get around to it, another disk in the storage
> system also dies. Poof.
> 
> We have replaced that entire group now with a RAID 10. We no
> longer have any RAID 5 setups.
> 
> Learn from our mistakes; don't use RAID 5 unless you can afford
> to throw away that data and the time it takes to restore from
> backup.
> 
> (Other lesson you should already know: RAID is not a backup
> system.)
> 
> -dsr-
> 
> --
> http://tao.merseine.nu/~dsr/eula.html is hereby incorporated by
> reference.
> You can't defend freedom by getting rid of it.
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