On Fri, 13 Aug 1999, James Manning wrote:
To be honest, I'm still a little confused that I can't seem to find
any s/w h/w combination that will yield better than 30MB/sec
writes to 20 drives (18.2GB Cheetah-3's operating over 2 channels,
both at 80MB/sec with LVD). Any tips? s/w raid stripe size
should be (# of h/w raids) * (h/w raid stripe size)? or should
it be (# of physical drives) * (h/w raid stripe size)?
a cheetah can transfer about ~16-18MB sustained.
so you really don't want more than 4 drives per channel or you'll
start to lose out. And that's ignoring the overhead of 4 very active
(under RAID) drives on one bus.
You've got 10 drives per bus, so probably your drives are crowding
each other out. Get some more scsi controllers for really optimal
hardware configuration. Eg for 20 drives you probably want at least 4
seperate channels. (Tekram have nice sym53c896 LVD cards at a good
price).
Another thing to look at is number of tagged commands. Most linux
scsi drivers (eg buslogic, sym53c8xx) allow you to raise the max
number of queued commands from the (usually conservative) default.
Raise it to something like 50 or 60. This will give each drive more
meat to chew on, and hopefully reduce bus contention a little bit.
finally, consider enabling the drives write-caching (usually off by
default). There's a tool on sunsite/metalab called scsi-info iirc
which will allow you to do this. Has a nice tk/tcl gui aswell. If you
this make sure you've got a good UPS. :)
hth's.
regards,
--
Paul Jakma
[EMAIL PROTECTED] http://hibernia.clubi.ie
PGP5 key: http://www.clubi.ie/jakma/publickey.txt
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