I have two LTO-3 (QUANTUM ULTRIUM 3) drives attached to a dual Adaptec
U160 controller (one per SCSI host) on a Dell PE2850 running a RHEL4
based kernel (2.6.9 based).
I'm trying to read (with tar) LTO-3 tapes written on another system
(possibly an SGI IRIX box), but I'm getting extremely variable read
rates - from a few Kb/s to tens of Mb/s - while reading the same tape
After a bit of trial and error, it looks like the tapes have been
written in variable block mode with a block size of 16Kb
To list the tapes, I need to set the block size to 0 (mt setblk 0) and run:
tar tvfb $TAPE 32
Running strace on the tar process shows that it does a number of
read()'s then 'sticks' on a read() for a number of seconds, and then
does a burst of read()'s - the number of reads it does in these bursts
and the time if waits on a particular read vary.
My guess this is something to do the drive having to repositioning the
tape between reads and breaking the tape streaming ...
I get the same issue on both drives with different tapes from the same
source.
I am using the default st module options and not doing anything other
than using 'mt setblk 0'.
Is there anything I can do to get a decent, sustained read rate from
these tapes?
Thanks
James Pearson
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