Linux on PE2950, PV220S and very slow PV124T

[John LLOYD]

> Tape write and read are very slow.
> This was a bit better a mounth ago, since a power outage, 
> system seems 
> to be slow, but I can't figure out why !
> 
> Tape write :
> Quite simple, reading files from PV220S to LTO3 Tape.
> For a 300 GB of data transfert (lots of files, around 12M), it take 
> around 20 hours !
> 
> Backup to tape through tar :
> mt -f /dev/st0 setblk 0
> tar -b 128 -cvf /dev/st0 /my_backup_dir
> 

You should be able to read the tape quickly, if the hardware is good:

 % tar -tbf 128 /dev/st0

Note that the blocking factor should not matter much for performance, it
is not really necessary.

Your command syntax is not, strictly speaking, correct (see info tar for
details).  you should spell this

 % tar -cvbf 128 /dev/st0 /my-backup

that is, put the function letter "c" first.

Also, check value of TAR_OPTIONS; if you have compression or other
things turned on then this may be affecting performance by not blocking
the data to 128 blocks, for example.


Another test, which avoids questions of filesystem state, disk
throughput, etc, is simply to dd to the tape device.  This should run
really fast due to ease of compression:

 % time dd if=/dev/zero of=/dev/nst0 bs=1M count=1000

a gig should take 10 to 20 seconds.


--John