In a cached disk subsystem, the write overhead of RAID 5 can be negated.
Hence the reason if a cache battery dies, write through cache mode is
enabled, as cache may not be able to be destaged in the event of a power
failure- this will have a massive effect on write wait time on the host.
Caught the backend of this discussion, what is the disk subsystem? What
are the symptoms of the problem?
_____________________________
Ian Smith
SAN/TSM Specialist
IT Infrastructure
Rabobank International
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Mailto: ian.smith AT rabobank DOT com
-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Matthew Glanville
Sent: 16 January 2006 16:47
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: [ADSM-L] AW: [ADSM-L] Backup / Restore IMAGE
"ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU> wrote on 01/16/2006
07:47:28 AM:
> On Jan 16, 2006, at 2:34 AM, Herrmann, Boris wrote:
>
> > ...I think the problem is the raid5 system....
>
> Boris - RAID 5's performance issues during write operations has been
> discussed many times on this mailing list. It is the nature
> of that technology, which is performance-expensive.
If it's hardware RAID-5 with RAM cache, it could be write caching is
turned off; either on purpose, by default, or from a bad or expired
battery. That greatly affects write speeds should be looked at before
blaming the RAID-5 entirely.
Matthew Glanville
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