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RAC and ASM disk layout [message #176634] Fri, 09 June 2006 00:50 Go to next message
Messages: 1
Registered: June 2006
Junior Member

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.

Re: RAC and ASM disk layout [message #176731 is a reply to message #176634] Fri, 09 June 2006 06:10 Go to previous messageGo to next message
Frank Naude
Messages: 4570
Registered: April 1998
Senior Member
Well, RAID-5 is already a form of redundancy. But if you need to have redundancy across storage cabinets, you need to define different ASM fail groups with normal or high redundancy.

W.r.t. the LUN's: I would imagine that the 100GB LUN would be better than several smaller ones. Either way, you wouldn't quite know on which disk your data is stored.

Maybe it's worth asking if the RAID-5 can be disabled on cabinet level. By doing so you will have more usable space and Oracle will have better control over where the data is stored.
Re: RAC and ASM disk layout [message #179318 is a reply to message #176731] Mon, 26 June 2006 20:44 Go to previous message
Messages: 2
Registered: June 2006
Junior Member
Create a LUN and create a ASM disk on top of it. Then create a ASM diskgroup with external redundancy disk. In this way you have EMC handle redundancy. There's not point to do mirror or redundancy in ASM level again on top of EMC RAID group.

Here is an example

1. Create ASMlib disk

/etc/init.d/oracleasm createdisk DSK_V1 /dev/cciss/c1d4p1
/etc/init.d/oracleasm scandisks
/etc/init.d/oracleasm listdisks

2. Create disk group
SQL> create diskgroup DG01 external redundancy disk 'ORCL:DSK_V1' ;

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