From: Holger.VanKoll@SWISSCOM.COM
Date: Thu Apr 24 2003 - 07:05:21 EDT
Hello,
from aix-docs:
Set maxpgahead to 16 times the number of disk drives (vmtune -R).
This causes page-ahead to be done in units of the stripe-unit size (64
KB) times the number of disk drives,
resulting in the reading of one stripe unit from each disk drive for
each read-ahead operation
Ok, that means with a stripe-size of 128kb I choose 32 times the number
of disk-drives, correct?
Now... I got several VG with striped FS, they contain different number
of disk-drives.
I am not sure what "number of disk drives" to choose.
8 VG have 5 drives, 2 have 4 drives, 1 has 10 drives.
If I set maxpgahead to 32*5, those 8 vg will perform well and the 1 with
10 will perform quite well, too.
If I set it to 32*10, the 8 vgs will still perform quite well and the 1
with 10 well, too. But I risk more unnecessary IO then with 32*5; and
especially on the 8VG this will increase disk-busy% (tm_acct).
So, 32*5 sounds good to me. What do you think?
But what about 32*4? The 2VG will perform well, but what about the 8VG
then? Will they perform at 4/5 as much as they would perform at 32*5 or
less?
I think it will be close to 4/5 but would like to hear your opinion.
Regards,
Holger
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