tape will not stream ...

[pdxcity]

Server ES40 4/833CPU/32GB RAM/Tru64 5.1B-3
HBA KZPCA-AX, Tape Drive HP DLT-8000
Only device on the bus
Cart is DLT-IV 40/80 brand new
Drive just cleaned w/new cleaning cart.

I can't get the tape to stream at all,
any suggestions ? Currently I'm getting
about 650-750 KB/sec with tar/default
blocks

cpu/disk loads are effectivly 0%

-pete

[Ivan Ferreira]

Do the following test:

tar cvf /dev/tape/tapeXc /usr

Don't forget the trailing "c". If you have a file system with big files, backup that file sytem.

Run collect to identify the throughput:

collect -st
collect -T

Post the results. Then, run

dia -R

To see if there are SCSI events related to the tape drive.

[pdxcity]

will see what collect has to say next
but did a quick foreach loop and
got the results in the attachment,
looks like tar's default block size
is just too small. Up to 4 MB/Sec not
the 6-12 MB/Sec the drive is suppose
to go but a lot better !

-pete

[Ivan Ferreira]

The problem could be the block size or the size of the files backed up. A lot of small files will take long time to backup.

If you want to do a performance test, you can use dd, for example:

dd if=/dev/zero of=/dev/tape/tapeXc bs=64k

Use collect to capture performance data.

[pdxcity]

well with /dev/zero of a file of nothing
but zero's and with hw compression i get
approx 12 MB/sec. With out compresson
approx 5.5 to 6 MB/sec, just what the
drive is suppose to do. The catch seems
to be keeping the block size BIG, at
least 60 KB.

btw, if your file is anywhere random,
like from gzipping it, dont use hw
compression, can get pretty slow, and
that is what I was doing with out thinking.

so, block size at least 60 KB, and think
about if you should use hw compression or
not.

collect as usual showed me all i needed
to know.

-pete

PS remember tar's blocks are 512 bytes