RE: RAC storage newbee question
- From: "Mark W. Farnham" <mwf@xxxxxxxx>
- To: <ckaj111@xxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 26 May 2014 13:37:15 -0400
It is hard to beat external redundancy on hardware enabled raid 1, duplex or
triplex. Raid 0 is a real puzzler, because when you play them on ASM and
string them together you probably end up slicing across each disk to have
small enough chunks to deal with. ASM will stripe across the disks you give
it. The best thing to give ASM is a single platter (or two or three platters
that operate duplex or triplex as the same unitary piece of acreage if you
go external.)
The complex cross hatch utilization pattern that may develop from handing
ASM disks that are already striped is just that: complex. It is not clear
whether you win or lose from mathematical modelling but there is potential
for lots of extra seeking at the physical spindle level when you're drinking
full 1MB or 4MB drinks. For little reads it is probably a wash, so my advice
is to avoid the possible unfortunate i/o pattern.
But this may vary with the precise disk farm configuration. Compared to
software raid, ASM might do better.
Is there no opportunity to spin up a test with your planned load?
Probably the most important thing about handing pieces of storage to ASM
from a pool is to make sure that the physical components underlying your
pieces are not simultaneously also in usage by any other loads (especially
loads that you cannot observe and control, which is frequently true if the
storage is being provided from a pool.)
mwf
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of Chris King
Sent: Monday, May 26, 2014 12:40 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: RAC storage newbee question
Thanks in advance for your feedback on this question.
We built RAC in a lab using VMs and now are planning to build on metal.
We're using ASM for disk storage management, so I requested raw disk.
I'm told by the storage admin that he can not provide raw disk. Although he
could provide raid 0.
So my question is:
If I ask the storage manager to provide disk that is already raid 0+1, and
then I create ASM disk groups using the "external" option. Is this approach
any better/worse than providing ASM raw disk to manage?
(I would use the external option so that I don't end up striping and
mirroring disk that is already striped and mirrored.)
Or would it be better to have him provide all the disks as raid0, and have
ASM handle all the redundancy?
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