Re: high load, no bottleneck

[Brian Buhrow <buhrow%nfbcal.org@localhost>]

        Hello.  thor's right. The raidframe driver defaults to a rediculously
low number of maximum outstanding transactions for today's environment.
This is not a criticism of how the number was chosen initially, but things
have changed.  In my production kernels around here, I include the
following option which is a number I derived from a bit of impirical
testing.  I found that for arrays of raid5 disks, I didn't get much benefit
with higher numbers, but numbers below this did show a marked decline in
performance.
For example, on an amd64 machine with 32G of ram, I have  a raid5 set
with 12 disks running on 2 mpt(4) buses.  I get the following read and
write numbers written to a filesystem with softdep enabled on top of a
dk(4) wedge built on the raid5 set:
(This is NetBSD-5.1)

test# dd if=/dev/zero of=testfile bs=64k count=65535
65535+0 records in
65535+0 records out
4294901760 bytes transferred in 125.486 secs (34226142 bytes/sec)


test# dd if=testfile of=/dev/null bs=64k count=65535
65535+0 records in
65535+0 records out
4294901760 bytes transferred in 5.994 secs (716533493 bytes/sec)

The line I include in my config files is:

options  RAIDOUTSTANDING=40 #try and enhance raid performance.