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
Thames Court, One Queenhithe
London EC4V 3RL
t: +44 (0)20 7809 3046
f: +44 (0)20 7809 3599
m: +44 (0)7843 689914
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
_____________________________________________________________
This email (including any attachments to it) is confidential, legally
privileged, subject to copyright and is sent for the personal attention of the
intended recipient only. If you have received this email in error, please
advise us immediately and delete it. You are notified that disclosing, copying,
distributing or taking any action in reliance on the contents of this
information is strictly prohibited. Although we have taken reasonable
precautions to ensure no viruses are present in this email, we cannot accept
responsibility for any loss or damage arising from the viruses in this email or
attachments. We exclude any liability for the content of this email, or for the
consequences of any actions taken on the basis of the information provided in
this email or its attachments, unless that information is subsequently
confirmed in writing. If this email contains an offer, that should be
considered as an invitation to treat.
_____________________________________________________________
|