[Bacula-users] Very slow speed writing to tape

Hi everybody,

I'm having speed/jamming issue when writing to my Dell PV124T which *seems*
to be related to Bacula. Basically, speed is really inconsistent, as in:

 Elapsed time:           10 secs
 SD Bytes Written:       920,245,603 (920.2 MB)
 Rate:                   92024.6 KB/s

 Elapsed time:           40 mins 53 secs
 SD Bytes Written:       72,574,315,017 (72.57 GB)
 Rate:                   29585.9 KB/s

 Elapsed time:           33 mins 40 secs
 SD Bytes Written:       2,402,398,034 (2.402 GB)
 Rate:                   1189.3 KB/s

 Elapsed time:           1 hour 10 secs
 SD Bytes Written:       18,271 (18.27 KB)
 Rate:                   0.0 KB/s

As you can see, the fastest is around 89 MB/s, but that is one of twenty
something migration. Now, that said, I've been testing multiple runs using
"dd if=/dev/zero of=/dev/nst0" and results are pretty consistent (between
120 - 143 MB/s).

 # dd if=/dev/zero of=/dev/nst0 bs=1024k count=50000
 50000+0 records in
 50000+0 records out
 52428800000 bytes (52 GB) copied, 367.916 seconds, 143 MB/s

 # dd if=/dev/zero of=/dev/nst0 bs=64k count=500000
 500000+0 records in
 500000+0 records out
 32768000000 bytes (33 GB) copied, 257.352 seconds, 127 MB/s


I don't know if it would help in that case but spooling is not enable. I'd
also like to know if it can be related to block size?

Can anybody point me to right direction to solve that problem. After many
google search I still haven't found any answer.

Here are some system information you might find useful:

OS: Ubuntu 7.10
Bacula version: 2.0.3 (From Ubuntu repository)

# uname -a
Linux **** 2.6.22-15-generic #1 SMP Fri Jul 11 19:25:33 UTC 2008 i686
GNU/Linux

# lspci
--snip--
09:08.0 SCSI storage controller: LSI Logic / Symbios Logic 53c1030 PCI-X
Fusion-MPT Dual Ultra320 SCSI (rev c1)

Bacula-dir.conf:
Device {
  Name = IBM-ULTRIUM-TD3
  Drive Index = 0
  Media Type = LTO-3
  Archive Device = /dev/nst0
  AutomaticMount = yes;               # when device opened, read it
  AlwaysOpen = yes;
  RemovableMedia = yes;
  RandomAccess = no;
  AutoChanger = yes
  LabelMedia = no;
}


Please note that our PV124T was recently completely replaced by another one.
The speed was slow before the replacement, and it is still after.

Please let me know if you need more information.


Thank you very much,

J-P



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