Topic: Tape backup/disk system performance

[bebran]

I've just installed an Adaptec 2940UW and an AIT-35 SCSI tape streamer on my server, but I'm not sure if the system is performing as expected.

System config.:
SME 6.01, dual 1 GHz Pentium III, 1 GB RAM, 1x 40 GB IDE-100 harddisk.

The tape streamer / SCSI adapter bandwidth is 20 MB/s and the IDE disk should have a 100 MB/s (Mbit/s ?) bandwith.

During backup my processors are not running over 20-30% at any time and I can't register any delays on serving web pages.

Why do'es it only give an average of 600 kB/s for a 12 GB backup - the backup is running for appr. 6 hours?? Theoretical it should be possible to backup 12 GB in 17-18 min.

Moving large files from my desktop PC to the server and visa versa only yields appr. 600 kB/s - so it's probably my disk system. Is there any special drivers/setup for supporting IDE-100 or....?

Best Regards
B.B.Andersen

[Boris]

You may want to check if DMA on your drive is enabled. Search for  DMA hdparm command and examples on this site.

[bebran]

Good point Boris.
Running 'hdparm -d /dev/hda' returns:

/dev/hda
 using_dma  =  1 (on)

So I recon this is not the issue - any more ideas?

[Curly]

My backups are just as slow as yours. I always thought that the way the backups were made was the main cause for slow backup performance.

(P3 - 933, 3x18.2 Gb SCSI 10.000 in Raid 5 , DAT 12/24)

It sure isn't caused by the disks (in my case), and when I do a simple tar to tape, the performance looks OK to me.

The normal backup makes a compressed (gzip) tar file, and that is probably to slow to keep the tape-drive in streaming mode. So the tape drive starts, stops, starts, stops and al the re-positioning of the tape takes lots of extra time.

You could test the disk / tape performance bij just tar-ring a big file to tape.

edit: found another topic discussing the same problem:

http://forums.contribs.org/index.php?topic=27431.0

[bebran]

Thanks Curly - just what I needed.
The link tells it all, I'll check it out tonight.