Re: asm disks
- From: Hans Forbrich <fuzzy.graybeard@xxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Mon, 04 Feb 2013 15:27:27 -0700
On 04/02/2013 1:37 PM, Mike Hayes wrote:
> It seems to me we have just gone against best practice. For those who have
> experience with ASM do you use hardware raid or not?
>
The 'common wisdom' is to use RAID 1+0 or RAID 5 and leave ASM at
External Redundancy.
Alex Gorbachev has an interesting presentation and demo in which he
demonstrates that RAID under Oracle can end up with data loss, if a
second or third disk goes out. Never say never - in a typical SAN, the
mean time betwen failure of any disk on the SAN is in the 'days' range,
and it is conceivable that a second disk supporting the database can
fail before the first is replaced and rebuilt.
On the other hand, ASM normal or high redundancy will stop the database
cold, raising an error and killing the DB processes, thereby
guaranteeing that there is no data loss. Transactions are either
committed, and therefore in the redundant redo logs, or not committed
and therefore thrown away.
His basic presentation can be seen at
http://www.nyoug.org/Presentations/2012/June/Gorbachev_Oracle_ASM.pdf -
but it really only hits home with the demo in which he kills several
disks at random (audience calls out which to kill) to prove the point.
So ASM does best with JBOD, normal or high redundancy and no RAID.
But of course, the common wisdom says use RAID 5 ... or if pushed (and
totally against the recommendation of the SAN administrator) perhaps 1+0.
/Hans
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