On Wed, Feb 04, 2004 at 10:49:01AM -0500, tobias.bluhm AT philips DOT com wrote:
> I'm slightly baffled at the Tape Time though - it seems to have gone down.
> I expected it to remain about the same, half the data at half the tape
> write speed.
[clip]
> Typical results with large backup run using hardware compression:
> Output Size (meg) 69757.9 57995.6 11762.3
> Original Size (meg) 69757.9 57995.6 11762.3
> Avg Compressed Size (%) -- -- -- (level:#disks ...)
>
> Tape Time (hrs:min) 3:02 2:16 0:46
> Tape Size (meg) 69757.9 57995.6 11762.3
> Tape Used (%) 100.0 82.9 17.1 (level:#disks ...)
> Filesystems Taped 93 19 74 (1:74)
> Avg Tp Write Rate (k/s) 6541.9 7264.8 4388.6
> One of the first runs using software compression:
> Output Size (meg) 27744.5 23489.8 4254.7
> Original Size (meg) 56949.0 45437.6 11511.4
> Avg Compressed Size (%) 48.7 51.7 37.0 (level:#disks ...)
>
> Tape Time (hrs:min) 1:25 1:08 0:17
> Tape Size (meg) 27744.6 23489.8 4254.8
> Tape Used (%) 57.8 48.6 9.2 (level:#disks ...)
> Filesystems Taped 91 27 64 (1:64)
> Avg Tp Write Rate (k/s) 5560.0 5919.3 4164.3
Doesn't look *too* mysterious. The spec'ed native SCSI rate for
an SDX-500 is 6MB/s, and on large files (the fulls) you get
exactly that, 5.9MB/s.
But your system is just not capable of feeding the SCSI interface on
the drive much faster than that. On the HW compression run, you know
you're getting at least 70/50 compression, so the tape drive should be
sucking data at 8.4MB/s, but you're only getting 7.2MB/s on large
files.
This could your SCSI controller, PCI congestion on the motherboard,
the kernel not recognizing the southbridge on the motherboard
optimally, etc.
Doesn't matter with your new configuration, though. You've got
(apparently) lots of client CPUs to spread the SW compression time
over, and you're saturating the tape drive with your precompressed
data, so all is good.
--
Jay Lessert jay_lessert AT accelerant DOT net
Accelerant Networks Inc. (voice)1.503.439.3461
Beaverton OR, USA (fax)1.503.466.9472
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