LSM striping across multiple SCSI controllers
=============================================
Hi,
I'm trying to build an LSM stripeset across multiple SCSI controllers (Note
No HSZ40 or RAID involved here).
I have 5 disks per stripeset and 2 SCSI controllers with 3 disks on one
controller and 2 disks on the other. I would like to build my stripeset with
the first stripe on the first disk on controller 1 and the second stripe on
the first disk on controller 2 etc but LSM does not seem to honour this.
Read on if you're not already bored...
I built the stripe volume using
# volassist -g btrmdg -U gen make log 512m alloc=0 align=0 layout=stripe \
nstripe=5 rz8 rz25 rz9 rz27 rz10
so I specified the order on the command line in which I wanted the stripes
to be placed.
i.e. put the first stripe on rz8 followed by rz25 then rz9 then rz27 and rz10.
Then I tested my nice new stripe with -
# dd if=/dev/rvol/btrmdg/log of=/dev/null bs=64k count=1
whilst running volstat in another window
# volstat -g btrmdg -d -i 1
Because I was using count=1 on dd and the default stripe width is 64k I should
only be accessing rz8, the first device in the stripe. However, you guessed
it, I saw rz10, and only rz10 being hit.
Okay - now step up the count on dd and check which disk gets hit next.
# dd if=/dev/rvol/btrmdg/log of=/dev/null bs=64k count=2
This time rz10 and rz25 were recorded as being accessed.
Next..
# dd if=/dev/rvol/btrmdg/log of=/dev/null bs=64k count=3
This time rz10, rz25 and rz27 were hit.
Summary
-------
It looks like the stripe width can only be built in alpha/numerical order
which is a shame 'cause I should get slightly better performance from my
stripe set if I can write to alternate controllers. Does anyone know of a
workaround for this?
Cheers
Keith McCabe
Banque Paribas Capital Markets
London W1
Received on Wed Mar 05 1997 - 12:40:11 NZDT