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I'm sure this is stuff I should know, but I've never been very good at
SCSI performance tuning.

I've got an i386 with some SCSI disks, and I'm working on building a
couple of RAID arrays.  The first array is up and working, and I don't
much care how fast it is.  The second, though, needs to be speedy.

Partial dmesg output follows:

NetBSD 1.5.1_ALPHA (GAMERA) #0: Tue Jan 23 11:43:12 MST 2001
cpu0: Intel Pentium II (Klamath) (686-class)
siop1 at pci0 dev 11 function 0: Symbios Logic 53c875 (ultra-wide scsi)
siop1: using on-board RAM
siop1: interrupting at irq 10
scsibus1 at siop1: 16 targets, 8 luns per target
siop0 at pci0 dev 14 function 0: Symbios Logic 53c875j (ultra-wide scsi)
siop0: using on-board RAM
siop0: interrupting at irq 9
scsibus0 at siop0: 16 targets, 8 luns per target
scsibus1: waiting 2 seconds for devices to settle...
siop1: target 0 using 8bit transfers
siop1: target 0 now synchronous at 20.0Mhz, offset 16
siop1: target 0 using tagged queuing
sd2 at scsibus1 target 0 lun 0: <IBM, DMVS36D, 0210> SCSI3 0/direct fixed
siop1: target 0 using 16bit transfers
siop1: target 0 now synchronous at 20.0Mhz, offset 16
sd2: 35003 MB, 11739 cyl, 20 head, 305 sec, 512 bytes/sect x 71687340 secto=
rs
siop1: target 1 using 8bit transfers
siop1: target 1 now synchronous at 20.0Mhz, offset 16
siop1: target 1 using tagged queuing
sd3 at scsibus1 target 1 lun 0: <IBM, DMVS36D, 0210> SCSI3 0/direct fixed
siop1: target 1 using 16bit transfers
siop1: target 1 now synchronous at 20.0Mhz, offset 16
sd3: 35003 MB, 11739 cyl, 20 head, 305 sec, 512 bytes/sect x 71687340 secto=
rs
st0 at scsibus1 target 5 lun 0: <HP, C1557A, U812> SCSI2 1/sequential remov=
able
st0: siop1: target 5 now synchronous at 10.0Mhz, offset 16
density code 37, variable blocks, write-enabled
ch0 at scsibus1 target 5 lun 1: <HP, C1557A, U812> SCSI2 8/changer removable
ch0: 6 slots, 1 drive, 0 pickers, 0 portals
scsibus0: waiting 2 seconds for devices to settle...
siop0: target 0 using tagged queuing
sd0 at scsibus0 target 0 lun 0: <SEAGATE, ST34572W, 0784> SCSI2 0/direct fi=
xed
siop0: target 0 using 16bit transfers
siop0: target 0 now synchronous at 20.0Mhz, offset 15
sd0: 4340 MB, 6300 cyl, 8 head, 176 sec, 512 bytes/sect x 8888924 sectors
siop0: target 1 using tagged queuing
sd1 at scsibus0 target 1 lun 0: <SEAGATE, ST32272W, 0784> SCSI2 0/direct fi=
xed
siop0: target 1 using 16bit transfers
siop0: target 1 now synchronous at 20.0Mhz, offset 15
sd1: 2157 MB, 6300 cyl, 4 head, 175 sec, 512 bytes/sect x 4419464 sectors

In a nutshell, the problem is this:  sd2 and sd3 are getting a
throughput rate of about 1MB/s.  I have another disk in the office,
though, which can get about 9MB/s.  (This is measured with "dd
if=3D/dev/zero bs=3D1024k count=3D100 of=3D/dev/sd?d".)  The other (fast) d=
isk
is a year-old Seagate Barracuda, if that helps any.  I'm using the
same enclosures and cables, so I just don't see what would make the
difference here.  To make matters more confusing, I have another,
identical Barracuda which runs at 1MB/s.

Any thoughts on what's going on here?

Chris

--=20
---------------------------------------------------- chris@cjones.org
Chris Jones                                          Mad scientist at large
  www.netbsd.org www.postgresql.org www.schemers.org www.python.org

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