From: Holger.VanKoll@swisscom.com
Date: Fri Oct 11 2002 - 13:13:29 EDT
after doing some testing I assume the following:
1) If the lv is striped, aix-lvm will start the reads on all drives
simultaneously.
2) If the lv is only distributed among several pv, it will read the pps
on the first pv, and then read the pps on the second pv etc.
Its hard to find this out reliably by testing... I would be easier if
there were strip-sizes at 4mb (that would correspond to the pp-size)...
Thats why I am not sure here.
If I am right, that would mean that one gains nothing by this "poor-mans
stripe" in almost any cases.
Can anyone confirm my assumption? I am quite sure about 1) but not about
2)
-----Original Message-----
From: Green, Simon [mailto:SGreen@KRAFTEUROPE.COM]
Sent: Friday, October 11, 2002 6:32 PM
To: aix-l@Princeton.EDU
Subject: Re: migrating a filesystem/lv from one disk to two
disks
The difference is in the stripe size. Doing striping at the
partition level gives you strips of, say 16MB. A proper striped LV will
have stripes of a few kB. An I/O operation will only benefit from
striping if it is writing data that spans two stripes. That's not
terribly likely with a 16MB stripe; probably only going to affect
backup/recovery and things like tablespace scans.
With a smaller stripe, many more I/O operations will be able to
benefit.
I can't comment on which is best for you.
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: Holger.VanKoll@SWISSCOM.COM
[mailto:Holger.VanKoll@SWISSCOM.COM]
Sent: 11 October 2002 12:43
To: aix-l@Princeton.EDU
Subject: Re: migrating a filesystem/lv from one disk to two
disks
>Another option would be to delete the filesystem,
recreate it
Well, I thought about this. I could create a "real"
striped lv/filesystem then.
However, I never tested the performance of a striped LV
versus a LV thats distributed manually between several volumes?
Is this a big difference in performance? What is the
technical difference at all?
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