Re: ASM diskmanagement and AIX 5.3

From: James Lorenzen <lorenzen_at_tiny.net>
Date: Mon, 01 May 2006 10:41:12 -0500
Message-ID: <125cavjh96j1ld9@corp.supernews.com>

Response below -
nospam wrote:

> <erikw_nl_at_yahoo.com> wrote in message
> news:1146483899.616571.94220_at_i39g2000cwa.googlegroups.com...
> 

>>Hi,
>>
>>We are using Oracle/RAC 10GR2 with ASM for disk management of diskspace
>>
>>used by the database. ASM requires that the disks are NOT included in a
>>
>>volume group and also uses the first block of the disk to store
>>essential information. RAC 10GR2 does not need HACMP anymore.
>>This setup imposes a serious problem for AIX systemmanagement:
>>1) It is difficult to distinguish disks on the AIX servers since they
>>are not part of a volume group.
>>2) The usage of the first block by Oracle implies that chdev may not be
>>
>>used to create a PVID, since chdev overwrites the first block. If chdev
>>
>>is being used on a ASM disk, Oracle can not read that disk, and the
>>database is lost.
>>3) Since ASM disks are writable by all servers in the cluster,
>>reserve_policy is switched off, the probability that a disk is by
>>accident used for a volume group is not unthinkable, with fatal
>>consequences for the database.
>>4) Changes in SAN configuration may imply that existing devices have to
>>
>>be rearranged with rmdev. Rmdev removes disk devices and other devices
>>nodes in /dev having equal major/minor number. Using sybolic names for
>>hdisk devices in the Oracle database by creating devices nodes in /dev
>>is not a viable option.
>>
>>Question:
>>Does anybody recognise these issues, and is there a workaround so that
>>ASM gets better integrated into standard AIX system management ?.
>>
>>Thanks in advance.
>>
>>
>>Erik
>>

> 
> 
> yes - i've seen this happen too...
> A LUN used by ASM is added to a VG - resulting in corruption.
> 
> This is what I've heard - so I might be wrong here - if so, please elaborate
> because
> I'm also very interested in this issue :
> Normally ASMlib should take care of this - Oracle relies on the
> vendors to provide OS specific implementations of ASMlib - however,
> none have done so and they have taken Oracle's linux implementation without
> really
> bothering. That means that :
> - it works fine on linux
> - might not work as expected on commercial unices ...
> 
> 

I have found that (on Solaris and Linux without ASMLIB) that creating a "small" partition first on the disk; one cylinder seems to be the smallest. Then the second partition may encompass the rest of the disk (LUN). This does not solve all the management problems, but it will "protect" ASM from the first block overwrite.

HTH
   James Received on Mon May 01 2006 - 10:41:12 CDT