Tape drive performance drops by 1/2

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To: sunmanagers@sunmanagers.org
Date: Fri, 1 Aug 2003 13:05:51 -0500

E450
Solaris 8
L400 library with dual mammoth drives
HVD(Differential scsi controller)
Both Mammoth drives are connected to the same controller

One tape drive got replaced last week and since then, backup performance
has gone down by 1/2 when both drives are used at the same time.

I'm using iostat to watch /dev/rmt/1 and /dev/rmt/0. When writing to one
drive is get about 3400-4200KB/Sec. Now if both drives are being written
to i get something like 2009KB/Sec on one drive and 1984KB/Sec on the
other. Then if i go back to writing to a single drive is get
3400-3900KB/Sec again on the single drive.

It doesn' matter if i use netbackup or /usr/bin/tar i get the same
results.

It's almost like the scsi controller can only write at 4MB/Sec. What i
think is the doc for the card states the following:
SCSI synchronous transfer rate 20/40 Mbytes/sec (Narrow/Wide)
SCSI asynchronous transfer rate <= 5 Mtransfers/sec (cable dependent)

Could the card be switching to asynchronous mode with the addition of the
new drive?

I was wondering if anyone else got this problem?

I'm also wondering how to find out which scsi card i have and what patches
apply to the card
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