In seeing writeup 3/17 attached below on this subject,
checked with our in-house AIX support team
on mirroring of page space.
The following 3/24 note discusses why our servers have mirrored page space.
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Sent: Monday, March 24, 2003 3:31 PM
To: Stenson, Ann M
Subject: Mirroring Paging Space
Hi Ann,
Yes we do mirror paging spaces and the root volume group on the Netview
servers.
When the paging device is mirrored, there will be extra write cycles as the
mirrored image of the paged memory is written to disk. This will affect the
performance to a slight degree. But using this same logic, the mirroring in
all cases affects performance to a slight degree.
Not mirroring paging space defeats the purpose of rootvg mirroring, which is to
keep a system or program active if a disk were to fail.
If our paging spaces were not mirrored but all the other logical volumes in
rootvg were mirrored, then the behavior of the system would be equal to that of
a non-mirrored rootvg that experiences a paging disk fail in the middle of
operation.
We avoid this by mirroring rootvg and paging spaces. If we loose a disk in
the root volume group we can replace the disk with out having a system crash.
So I disagree, you do want to mirror a paging space!
Thanks,
AIX team
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forwarded to in-house AIX team
-----Original Message--------------------------------
From: Stephen Hochstetler [mailto:shochste AT us.ibm DOT com]
Sent: Monday, March 17, 2003 11:19 AM
To: nv-l AT lists.tivoli DOT com
Subject: Re: [nv-l] Mirroring Paging Space
There is a book called "AIX Performance Tuning" by Frank Waters that would
be good for you to have as a resource.
You don't want to mirror a paging space. Waiting for the mirror to
complete writing would slow page space access. Idealy you would have
multiple paging spaces across several drives. All of them would be the
same size except the first one. That is because only the first one is
available at boot time, so all used page space is from the first one during
boot. After that they are round-robin used.
Kind regards,
Stephen Hochstetler shochste AT us.ibm DOT com
International Technical Support Organization at IBM
11400 Burnet Road Austin, TX 78758
Office - 512-838-6198 (t/l 678) FAX - 512-838-6931
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http://www.redbooks.ibm.com
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