Strange disk performance on a DS 5000

[Mike Iglesias]

We've been doing some crude disk performance tests on our DECstation 5000/200
with several drives:  DEC RZ55, CDC Wren IV (94171) and Maxtor XT-8380S.
The performance we have seen for the CDC and Maxtor drives is very slow,
considering that they are supposed to be able to do synchronous transfers.
One crude test we've done is using "dd" to read the raw disk and
dump it to /dev/null.  A dump of the a partition produces the following
transfer rates (all approximate):  RZ55 - 1.5mb/sec, CDC - 394kb/sec,
Maxtor - 394kb/sec.  On a Sun Sparc, the CDC disk will do about 770kb/sec.

We're running a kernel with SCSI_TRYSYNC set for the "unknown" disk
type in scsi_data.c.  On a CDC Wren VI (650mb) drive, we can get about
1.5mb/sec transfer rate using dd, so we're pretty sure Ultrix is
trying to do sync transfers. 

Is there something about the CDC/Maxtor drives that doesn't get along
with Ultrix?  Are there some parameters (/etc/disktab block size and
fragment size?) that need to be changed?  



Thanks,


Mike Iglesias
University of California, Irvine
Internet:    iglesias at orion.oac.uci.edu
BITNET:      iglesias at uci
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