Re: Oracle RAC and raw disks
- From: "Jackson, James D. (Mission Systems)" <James.D.Jackson@xxxxxxx>
- Date: Thu, 6 Apr 2006 14:27:00 -0600
I'm not questioning whether raw devices are OK. I understand their performance benefits and their management challenges. I was merely trying to point out what factors might be underlying the DBA's motivation to use Oracle to manage the raw devices, essentially taking the storage management task out of the hands of the sysadmins.
AIX-Geek's issue of having storage that's not managed by AIX is a valid one, and can only be reconciled through appropriate system management procedures, unless Oracle's ASM has some sort of means of preventing AIX from creating volume groups on ASM-managed resources, which I doubt.
The problem is, the DBA can use ASM to circumvent the "typical" AIX-centric process for creating raw logical volumes that you described in your reply. ASM can use the raw disk devices directly to carve out its storage. It doesn't "need" logical volumes; it creates its own disk groups and storage containers. However, from LVM's point-of-view, the disks used by ASM are still available for assignment to a volume group, and if an unaware SA were to do so, the results would be catastrophic to the ASM storage containers.
This is, of course, assuming that his customer's DBA wants to use ASM to manage Oracle's storage, which appears to be the case.
-----Original Message-----
From: IBM AIX Discussion List [mailto:aix-l@xxxxxxxxxxxxx] On Behalf Of Gergely Fóti
Sent: Thursday, April 06, 2006 4:17 AM
To: aix-l@xxxxxxxxxxxxx
Subject: Re: Oracle RAC and raw disks
Even when the Customer uses Oracle9 or earlier release, raw devices are OK. You can win some performance without using file cache. But 1.) the other hand Oracle (10g) runs well with ASM; 2.) there's no problem with datafiles on file system. It is question of VMM tuning.
The raw device does not deal with hdisk at all. You make a VG, assign hdisks with that, then define LVs (as large as you wish, LV type not count, it can be anything). The raw device means the defined LV with "r" prefix (/dev/r<logical volume>), you have to refer this, when you are adding devices to database. Besides it must have readable/writable to user oracle.You cannot harm VG nor hdisk nor LV, when it is in use, so sysadmins are quite in safe. Any more questions?
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