Re: Slow restoration question - Mailing list pgsql-performance

RAID 10 is better than RAID 0+1.  There is a lot of information on
the net about this, but here is the first one that popped up on
google for me.

http://www.pcguide.com/ref/hdd/perf/raid/levels/multLevel01-c.html

The quick summary is that performance is about the same between the
two, but RAID 10 gives better fault tolerance and rebuild
performance.  I have seen docs for RAID cards that have confused
these two RAID levels.  In addition, some cards claim to support RAID
10, when they actually support RAID 0+1 or even RAID 0+1 with
concatenation (lame, some of the Dell PERCs have this).

RAID 10 with 6 drives would stripe across 3 mirrored pairs.  RAID 0+1
with 6 drives is a mirror of two striped arrays (3 disks each).  RAID
0+1 (with concatenation) using 6 drives is a mirror of two volumes
(kind of like JBOD) each consisting of 3 drives concatenated together
(it's a cheap implementation, and it gives about the same performance
as RAID 1 but with increased storage capacity and less fault
tolerance).  RAID 10 is better than RAID 5 (especially with 6 or less
disks) because you don't have the performance hit for parity (which
dramatically affects rebuild performance and write performance) and
you get better fault tolerance (up to 3 disks can fail in a 6 disk
RAID 10 and you can still be online, with RAID 5 you can only lose 1
drive).  All of this comes with a higher cost (more drives and higher
end cards).

-- Will Reese http://blog.rezra.com


On May 2, 2006, at 1:49 PM, Mark Lewis wrote:

> They are not equivalent.  As I understand it, RAID 0+1 performs about
> the same as RAID 10 when everything is working, but degrades much less
> nicely in the presence of a single failed drive, and is more likely to
> suffer catastrophic data loss if multiple drives fail.
>
> -- Mark
>
> On Tue, 2006-05-02 at 12:40 -0600, Brendan Duddridge wrote:
>> Everyone here always says that RAID 5 isn't good for Postgres. We
>> have an Apple Xserve RAID configured with RAID 5. We chose RAID 5
>> because Apple said their Xserve RAID was "optimized" for RAID 5. Not
>> sure if we made the right decision though. They give an option for
>> formatting as RAID 0+1. Is that the same as RAID 10 that everyone
>> talks about? Or is it the reverse?
>>
>> Thanks,
>>
>> ____________________________________________________________________
>> Brendan Duddridge | CTO | 403-277-5591 x24 |  brendan@clickspace.com
>>
>> ClickSpace Interactive Inc.
>> Suite L100, 239 - 10th Ave. SE
>> Calgary, AB  T2G 0V9
>>
>> http://www.clickspace.com
>>
>> On May 2, 2006, at 11:16 AM, Jim C. Nasby wrote:
>>
>>> On Wed, Apr 26, 2006 at 05:14:41PM +0930, Eric Lam wrote:
>>>> all dumpfiles total about 17Gb. It has been running for 50ish hrs
>>>> and up
>>>> to about the fourth file (5-6 ish Gb) and this is on a raid 5
>>>> server.
>>>
>>> RAID5 generally doesn't bode too well for performance; that could be
>>> part of the issue.
>>> --
>>> Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
>>> Pervasive Software      http://pervasive.com    work: 512-231-6117
>>> vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461
>>>
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