Re: RAC and ASM disk layout
- From: "Alex Gorbachev" <gorbyx@xxxxxxxxx>
- To: HELMUT.DAIMINGER@xxxxxx
- Date: Fri, 9 Jun 2006 16:55:25 +0200
Helmut,
Be careful with mirroring over two boxes using ASM - it can be quite a
surprise for you. I have mentioned that alrady couple times on this
list. See http://oracloid.blogspot.com/2006/05/vldb-with-asm.html.
Also be careful how storage chunks the space for LUNs. I know the case
when Clarion was actually forming LUNs using 128K chunks and on host
it was striped with 128K as well. This caused the problem in certain
circumstances (and might give you headach for fine striping in ASM). I
think it should be safer to use 1M chunks on storage box. At least,
this is the fixed size for allocation in ASM.
Regarding number of LUNs - I would go with multiple becuase in this
case you have chance to relayout easilly using rebalance feature of
ASM. Since you want to chunk all things on one RAD5 group - I am sure
it's a recepie for disasted... well, depending how hard you are going
to kick it.
MfG,
Alex
2006/6/9, Daiminger, Helmut <HELMUT.DAIMINGER@xxxxxx>:
Hi!
We are new to RAC and are discovering serveral uncertainties regarding
the best disk layout to use for ASM. We are running two EMC Clariion
systems (under RAID-5) and want ASM to write to both Clariions
simultaneously (i.e. use normal redundancy). ASM will balance the load
across the two failover groups (i.e. two LUNs) which reside in two EMC
Clariion arrays.
The question is, whether it is better to use a single LUN with 100 GB or
have a number of smaller LUNs (totalling 100 GB). Since we are using a
single raid group (i.e. 5 disks) for all database storage, all LUNs will
end up on the same physical devices anyway. So it might be harmful
having ASM to try and balance I/O across several LUNs which all reside
on the same physical devices.
This is 10.2 on HP-UX 11.23.
Thanks,
Helmut
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Best regards,
Alex Gorbachev
http://oracloid.blogspot.com
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