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Hi all. Discovered recently that our bonehead previous admin turned
off mirroring for a bunch of LVs (all software mirrored...dont ask)
and in the process of remirroring many important things, I got to
wondering if I should mirror page space? Downsides, upsides, etc...?

In article <a5e13cff.0408271324.404a2a36@posting.google.com >, sumGirl <emebohw@netscape.net> wrote:
> Hi all. Discovered recently that our bonehead previous admin turned
> off mirroring for a bunch of LVs (all software mirrored...dont ask)
> and in the process of remirroring many important things, I got to
> wondering if I should mirror page space? Downsides, upsides, etc...?

The general rule of thumb:

Mirroring page space is ok.

Mirroring dump device LV is not.

I don't have a strong opinion for or against mirroring page space, so I
mirror all rootvg LVs except for the dump LVs.

-Dan

On Fri, 27 Aug 2004 22:08:55 +0000 (UTC), Dan Foster
<usenet@evilphb.org> wrote:

>In article <a5e13cff.0408271324.404a2a36@posting.google.com >, sumGirl <emebohw@netscape.net> wrote:
>> Hi all. Discovered recently that our bonehead previous admin turned
>> off mirroring for a bunch of LVs (all software mirrored...dont ask)
>> and in the process of remirroring many important things, I got to
>> wondering if I should mirror page space? Downsides, upsides, etc...?
>
>The general rule of thumb:
>
>Mirroring page space is ok.
>
>Mirroring dump device LV is not.
>
>I don't have a strong opinion for or against mirroring page space, so I
>mirror all rootvg LVs except for the dump LVs.
>
>-Dan

Mirroring page space is not just OK its required if you don't want you
machine to panic if you loose a disk. Think about it, you only have
page space on hdisk0 and none on hdisk1. hdisk0 dies and along with
it goes your virtual memory.

As for dump devices, I'm pretty sure it's OK to mirror it now, as the
default dump device is hd6 (page space). What I tend to do now, as
you normally have loads of space on rootvg disks, is create 2 new dump
devices, one on disk0 and one on disk1, not mirrored, and tell the
system that one is primary and one is secondary. That way you will
always get a dump, and you don't need to introduce the bootup delay in
copying the dump from page space when the system comes back up. You
can copy it when the machine is back up.

Steven

mirror hd6, cos if you loose primary paging space, then your system
will hang or crash, this is not the case with secondary paging space
unless you fill all your paging space etc... I would mirror hd6 and
have 2 secondary paging spaces on different disks of the same size if
your worried about it. you have to remember that paging space is a
failsafe .. you need to spec you machine with enough memory yto stop
you having to use paging space. disk latency is 10,000 slower than
memory latency, so you are never going to perform if you start paging
out to paging space. you have to check your vmtune / vmo settings to
make sure maxperm and minperm are set correct for your workload also,
so read up on maxperm/minperm.

Rgds
Mark Taylor

A good and simple way is to use the mirrorvg command. Just type mirrorvg
rootvg, it will mirror everything on it with the proper options. It will
also remove the quorum if you have less than three disks in rootvg. It works
also on partially mirrored vg, mirroring everuthong needed.

And in fact, this command mirrors page spaces.

Regards



Tél : 06 14 99 80 94
e-mail : etienne.guillaumont@tiscali.fr
"sumGirl" <emebohw@netscape.net> a écrit dans le message de
news:a5e13cff.0408271324.404a2a36@posting.google.c om...
> Hi all. Discovered recently that our bonehead previous admin turned
> off mirroring for a bunch of LVs (all software mirrored...dont ask)
> and in the process of remirroring many important things, I got to
> wondering if I should mirror page space? Downsides, upsides, etc...?

emebohw@netscape.net (sumGirl) wrote in message news:<a5e13cff.0408271324.404a2a36@posting.google. com>...
> Hi all. Discovered recently that our bonehead previous admin turned
> off mirroring for a bunch of LVs (all software mirrored...dont ask)
> and in the process of remirroring many important things, I got to
> wondering if I should mirror page space? Downsides, upsides, etc...?

If you mirror your paging space(s), remember you'll incurr two disk
writes. All of my paging spaces are un-mirrored, in fact, I've
created 4 of equal sizes.

HTH,
pete's

"Pete's" <empete2000@yahoo.com> schrieb im Newsbeitrag
news:6724a51f.0409020609.6c48f5e9@posting.google.c om...
> emebohw@netscape.net (sumGirl) wrote in message
news:<a5e13cff.0408271324.404a2a36@posting.google. com>...
> > Hi all. Discovered recently that our bonehead previous admin turned
> > off mirroring for a bunch of LVs (all software mirrored...dont ask)
> > and in the process of remirroring many important things, I got to
> > wondering if I should mirror page space? Downsides, upsides, etc...?
>
> If you mirror your paging space(s), remember you'll incurr two disk
> writes. All of my paging spaces are un-mirrored, in fact, I've
> created 4 of equal sizes.
>
> HTH,
> pete's

Hi Pete,

Did you read through this thread? ;-) Let me deliver a short summary of
what has been discussed so far.
1) Paging space is memory. If you lose your unmirrored disk with a used
paging space you lose memory. Try to think about what consequences that
could have.
2) AIX defaults to mirror paging space since at least 4.3.2 for this reason.
3) The biggest advantage of using mirrorvg is that you cannot forget to
mirror your paging space(s) and the jfs log. Using it (together with
unmirrorvg) will safe you from many headaches.
4) To minimize impact of paging space reads/writes place paging space in
center or middle area of disk. Make sure all paging space partitions are
contiugous.
5) More than one paging space per disk is almost never necessary and in most
cases wrong.

HTH,
Andreas