Date: Sat, 28 Jul 2001 16:48:47 +0200 From: "Jose M. Alcaide" <jose@we.lc.ehu.es> To: hardware@FreeBSD.org Subject: DLT 4000 throughput and cstream Message-ID: <3B62D0CF.27C12B9@we.lc.ehu.es>
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Hello,
I am trying to maximize the data transfer rate to a DLT 4000 tape unit:
ahc0: <Adaptec 2940 Ultra SCSI adapter> port 0xdc00-0xdcff mem 0xdffff000-0xdfffffff irq 10 at device 10.0 on pci0
sa0 at ahc0 bus 0 target 5 lun 0
sa0: <Quantum DLT4000 D782> Removable Sequential Access SCSI-2 device
sa0: 10.000MB/s transfers (10.000MHz, offset 15)
I am pipelining dump(8) to cstream (ports/misc/cstream), using this
command line:
dump 0fua - <filesystem> | cstream -v 1 -b 64k -B 1m -c 2 -o /dev/nsa0
However, I am getting what a I think is a too low transfer rate
(compression is enabled on the DLT unit). This is what I get with
iostat(8):
sa0
KB/t tps MB/s
60.59 22 1.31
60.59 22 1.31
61.05 22 1.31
60.62 22 1.32
60.59 22 1.31
...
I tried several combinations of buffer sizes to no avail. Is this the
expected throughput for a DLT 4000? If it is not, what could I do for
obtaining higher data rates?
(Note: the disk is fast -two IBM DTLA's mirrored with Vinum-, and the
machine is an Athlon @ 800 MHz).
TIA,
-- JMA
****** Jose M. Alcaide // jose@we.lc.ehu.es // jmas@FreeBSD.org ******
** "Beware of Programmers who carry screwdrivers" -- Leonard Brandwein **
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