Suggestions to improve disk I/O speed

Álvaro Palma apalma at
Wed Oct 22 09:18:00 CDT 2003

I've a PowerEdge 1400SC, PERC3/DCL and 4x18GB 10Krpm U160 SCSI disk, in 2 RAID 1
mirrors, running RH 7.2 and stock 2.4.20-20.7 custom kernel, with megaraid
2.00.9 replacing original 1.18f, 1.5GB RAM 

This server runs Oracle 8i, and the problem is that, in heavy load, the disk
that contains the data (/dev/sdb, separated from OS and other, but in the same
SCSI channel of the controller) slow down its transfer ratio from 40MB/s to
10MB/s or less (measured using hdparm), obviously compromising seriously the
performance of the system.

My question is: Do you have any ideas to improve the performance that doesn't
involve traumatic changes? I'm trying to get the money to migrate to PERC4/SC
and RH 3.0, but meanwhile, I'd like some ideas.

I've think in move the second array to second SCSI channel in the controller,
but really don't know if this need any further settings besides putting the
cable in place. Or maybe this compromises the data? Any suggestions about what
can be done, some test that should be run? Or am I forced to move to newer
hardware? I know my problem is not CPU, average load always remain very (and
really very) low.

Thanks for your patience for such a long question.

Álvaro Palma

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