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List:       aix-l
Subject:    Re: RAID & HA
From:       Bruce Zimmer <b.r.zimmer () WORLDNET ! ATT ! NET>
Date:       2002-04-30 18:24:23
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The problem comes in that RAID5 does not perform very well without using a
write cache.  Since the write cache is on the RAID Adapter, there would be a
data integrity problem if a machine would fail over while there is still
data in the write cache.  There would be no way to "move" this data out to
its propler location on the disk platters or over to the other RAID
controllers write cache.  Products like the Shark and EMC Symmetrix use
complex interconects so that the disks are utilizing the same cache and if
one controller would fail the other has access to the cache.  Also, when the
docs say that RAID controllers can be used,  Is not plain striping RAID 0,
mirroring RAID 1.  These types of RAID controllers would not have the same
problems if they did not utilize a write cache.  Likewise a RAID 5
controller with write cache disabled would have no problems other than it
would be SLOOOOOOOOOOW.


Bruce Zimmer


----- Original Message -----
From: "Green, Simon" <SGreen@KRAFTEUROPE.COM>
Newsgroups: bit.listserv.aix-l
To: <aix-l@Princeton.EDU>
Sent: Tuesday, April 30, 2002 10:10 AM
Subject: Re: RAID & HA


> From the HACMP/ES 4.4 Installation guide:
> The HACMP/ES software supports the following disk technologies as shared
> external disks in a highly available cluster:
>  - SCSI-2 SE, SCSI-2 Differential and SCSI-2 Differential Fast/Wide
adapters
> and drives, including RAID subsystems.
>  - IBM SSA adapters and SSA disk subsystems.
>
> Obviously you may need to take special steps in configuring it all, but
> there's no reason you can't do it in principle.
>
> Simon Green
> Philip Morris ITSC Europe
>
> AIX-L Archive at http://marc.theaimsgroup.com/?l=aix-l&r=1&w=2
> AIX FAQ at http://www.faqs.org/faqs/aix-faq/
>
> N.B. Unsolicited email from vendors will  seldom be appreciated.
>
> > -----Original Message-----
> > From: Keith Reed [mailto:aixl@MAILMGR.COM]
> > Sent: 30 April 2002 14:58
> > To: aix-l@Princeton.EDU
> > Subject: RAID & HA
> >
> >
> > I have 2 H80s which I would like to set up in an HA config,
> > both sharing a 2104 SCSI Array set up as a RAID 5. I was told
> > that this was not possible; that if you have an HA setup, you
> > cannot have use RAID (or at least not SCSI; don;t know about SSA).
> > Can anyone confirm/deny this?
> >
>
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