Software RAID issues (was Re: Suggestions solicited, server bring up)

Bill McGonigle bill at bfccomputing.com
Sat Nov 21 18:02:52 EST 2009


On 11/21/2009 11:40 AM, Bruce Labitt wrote:
> Bill, why not RAID-5?  Isn't RAID-5 supposed to be ultra-reliable?  As 
> in hot swap disks?  Or does this just apply to software RAID-5...
> 
> -Bruce
> who knows very little about this RAID stuff...

RAID-5 itself has a problem known as the "RAID-5 write hole" where data
loss can be guaranteed in certain situations.  RAID-6 is a patch to
prevent this.

But RAID-5/6 also come with complexity, and software is buggy.  The main
advantage of RAID-5 is getting more disk space usable per dollar.  But
with cheap disk space under $80/TB RAID-1 (simple mirroring) gets you
less complex reliability and better performance.  And for a boot disk,
having only one surviving drive is sufficient to get your machine
running again.

ZFS's RAID-Z is probably the exception to the rule as everything is
round-trip checksummed, but I still wouldn't use it for a boot disk
since a boot disk set doesn't need to be big enough to justify any cost
savings.


-Bill

-- 
Bill McGonigle, Owner
BFC Computing, LLC
http://bfccomputing.com/
Telephone: +1.603.448.4440
Email, IM, VOIP: bill at bfccomputing.com
VCard: http://bfccomputing.com/vcard/bill.vcf
Social networks: bill_mcgonigle/bill.mcgonigle


More information about the gnhlug-discuss mailing list