Thanks for your response! Some info on the system: -Adaptec 29160N Ultra160 SCSI card - SONY SDT-7000 DAT tape * The tape is the only device on the SCSI bus. * Storing data to disk (with a 'tar cv --file=/dev/st0 ...') goes fast. Not a problem. * Restoring IS not good. As you sad, the drive is doing those 'little rewinds' and it is VERY slow. * I've seen the default module 'st' setting its default buffer size to 32 kb. Isn't that a bit small? Harry
-----Original Message----- From: Greg Freemyer [SMTP:freemyer@NorcrossGroup.com] Sent: Wednesday, June 26, 2002 4:48 PM To: Berge, Harry ten; SuSE general Subject: re: [SLE] module st
Harry,
Normally slow tape drives are caused by slow disk subsystems.
And when tape drives slow down, it is an exponential slowdown, not linear. This is due to the little rewinds that occur. I'm sure you can hear the difference between a tape drive that is streaming vs. one that is in stop/start mode.
The DDS2 with 2:1 compression runs at 3.6 GB/hr max. transfer rate.
To keep it running a full speed, it should have a 3x feed rate. That is 10.8 GB/hr.
Do a tar -cf /dev/null /your_data and calculate your feed speed.
If 10 GB per hour or faster you have a tape problem. Either hardware or config.
(A SCSI bus shared by the disk and tape is one of the possible problems. SCSI contention can slow things down even if the individual systems are fine.)
If 5GB / hour or less, you definitely have a disk sub-system that is just too slow, and this causes the tape performance to degrade drastically.
If between those numbers, it can be either.
In this case, perhaps you could insert a small buffer between your backup program and the tape. for example with bfr: http://www.glines.org:8000/software/buffer.html
This will be most useful when dealing with a large number of small files.
Greg Freemyer Internet Engineer Deployment and Integration Specialist Compaq ASE - Tru64 Compaq Master ASE - SAN Architect The Norcross Group www.NorcrossGroup.com
Hi,
I have a DDS2 drive attached to 7.3 pro, but the performance is very poor. At least for restoring. What are the correct parameters for the 'st' module to have at least some decent performance?
Now my colleagues are screaming that the tape drive works much faster under Windows :-(
Regards,
Harry ten Berge Test Engineer Holland Institute of Traffic Technology HITT B.V. P.O. box 717 Apeldoorn email :berge@hitt.nl <http://www.hitt.nl> tel : +31 555432537 fax : +31 555432554
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