streaming tape drive doesn't (did in 1.2, not in 2.4)

streaming tape drive doesn't (did in 1.2, not in 2.4)

Post by phil-news-nos.. » Wed, 15 Nov 2000 04:00:00



I haven't used one of these streaming tape drives since back on kernel
version 1.2.  Now I'm on 2.4 and I need to use this drive again.  But
now it's gotten really slow.

Previously, all I needed to do was make sure the userland process would
keep the write buffers full, and the drive would stream continuously.
That was in kernel 1.2 on a 33 MHz 486 and it was easy to do.  Now I'm
on a 400 Mhz Pentium II and nothing else running on the machine and it
just keeps jerking back and forth about every 32K bytes.

The drive is a QIC-150 in a Sun 411 box.  The kernel probes look like:

scsi0 : Adaptec AHA274x/284x/294x (EISA/VLB/PCI-Fast SCSI) 5.1.28/3.2.4
       <Adaptec AHA-294X SCSI host adapter>
scsi : 1 host.
  Vendor: ARCHIVE   Model: VIPER 150  21531  Rev: -004
  Type:   Sequential-Access                  ANSI SCSI revision: 01
Detected scsi tape st0 at scsi0, channel 0, id 5, lun 0
scsi : detected 1 SCSI generic 1 SCSI tape total.

One funny thing I noticed.  When I open the drive with O_SYNC, and write
in chunks of 512 bytes, it starts doing streaming for about 10 seconds
then falls back to jerky slow motion and stays there.

I've tried both sync and non-sync I/O, in blocksizes varying from 512 to
1048576.  Even at 1048576 it's jerking back and forth about every 32768
bytes (e.g. several times per single write() call).

The only thing that has changed, besides the kernel, is the SCSI controller
card.  I have an Adaptec 2940 (not U or W) now, and I had an Adaptec 1542C
previously.  But I would think the 2940 and its driver would be faster.

I'm also using /dev/zero as data source, so I would think it would be as
fast as it can be.

BTW, it streamed just fine on BSDi 2.0 and SunOS 4.1.3 back then.  I don't
have either of those now to try again, but I'll probably be giving OpenBSD
a try on this since I have it handy.

--
| Phil Howard - KA9WGN | My current websites: linuxhomepage.com, ham.org
| phil  (at)  ipal.net +----------------------------------------------------

 
 
 

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