From owner-freebsd-questions  Sat May 26 20: 7:39 2001
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Date: Sat, 26 May 2001 22:07:33 -0500
From: Dan Nelson <dnelson@emsphone.com>
To: Felix Hernandez <felix_hdez@yahoo.com>
Cc: Bill Moran <wmoran@iowna.com>, freebsd-questions@FreeBSD.ORG
Subject: Re: Slower tape drive when compression off
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In the last episode (May 26), Felix Hernandez said:
> root@oberon $$$ mt comp off
> root@oberon $$$ dd if=junk of=/dev/rsa0 bs=10k
> 51200000 bytes transferred in 20.322325 secs (2519397 bytes/sec)
> 
> root@oberon $$$ mt comp on 
> root@oberon $$$ dd if=junk of=/dev/rsa0 bs=10k
> 51200000 bytes transferred in 12.665153 secs (4042588 bytes/sec)

That's really weird.  A 10k blocksize is pretty small for DLT, though
(it's the default tar blocksize).  Try with a 64K blocksize, and tell
us your CPU speed.  A DLT8000 should be able to stream data at 6MB/sec
native, 12MB/sec if the data is compressible.  Maybe your hardware
isn't capable of sending data to the DLT fast enough to keep it
streaming.  Also see what a "dd if=/dev/zero of=/dev/rsa0 bs=64k" does;
maybe your disks are the bottleneck.  Turn compression off for this
test, of course :)

-- 
	Dan Nelson
	dnelson@emsphone.com

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