I have the same issue. I have a SDLT/320 tape drive, capable of 56 Gb/h. My 
holding disk is a two 73x10k Gb SCSI U320 Raid 0 array, and in my reports the 
total tape time is much smaller than the run time, since my tape writes at ~16 
MB/s and the dump speed to the holding disk performs only at (depending on the 
disk being dumped) 5-7 MB/s. I think the dumpers and the taper compete for 
I/Os, when they access the holding disk at the same time, the dumper for 
writing and the dumper for reading.

Cheers,

--
Iñaki Sánchez
Servicios Informáticos
Universidad de Navarra
Ed. de Derecho, Campus Universitario
31080 Pamplona (Navarra), España
tfno: +34 948 425600 Ext. 2106
http://www.unav.es/SI


Guy Dallaire wrote:

There was a recent discussion on the list regarding ultrium LTO3 tape
speed/performances.

According to my vendor, the LTO2 drive I'm about to buy is capable of
80Gb/Hour, that is approx 50 Mb/Sec if I'm right.

I'm currently using an adaptec AHA2940U adapter with my DLT4000 drive.
I think it's only capable of 20 Mb / Sec...

I have a couple of question:

What adapter should I buy to feed the LTO2 drive ? It need to be
compatible with centos 4.2 (RHEL 4 clone)

Provided I buy the correct adapter along with the tape drive, and my
holding disk is dedicated to amanda (it's a single 200 Gb ATA drive)
how am I to know (measure) if my tape server is feeding the tape drive
appropriately ? Would I be better using an SATA drive instead of an
ATA drive ?

Wouldn't the dumpers compete for I/O's on the holding disk with the
taper process ? Or does the taper process begins writting to tape only
when all the dumpers have finished ?

Where sould I look to see if my tape drive is fed properly ?

Thanks