* Joshua Baker-LePain <jlb17 AT duke DOT edu> [20070801 12:20]:
> On Wed, 1 Aug 2007 at 11:29am, Jean-Francois Malouin wrote

Hi Joshua,

> 
> >Hardware:
> >I've setup the default access device to the drives as non-compressing.
> >The library is hooked through a LSI U320 PCI-X scsi card to a 4
> >DualCore2 Xeon with 8GB of RAM running Debian/Etch running a 64bit
> >kernel 2.6.21.5-i686-64-smp. It should be beefy enough :)
> 
> If you ever want to use both drives simultaneously, you'll need a dual 
> channel SCSI card and each drive will need to be on its own channel. 
> Trust me on this one -- I tried every trick I could think of with 2 drives 
> on one channel (there should be plenty of bandwidth, right!?), but 
> couldn't get decent speeds when using both drives.

I tried running amtapetype simultaneously and on each tape on it's own
and I didn't see any differences in the transfer rates but since they
seem to throttle back to half-speed maybe I wasn't hitting their
bottlenecks.

> 
> >Running amtapetype with different blocksize gives me ~386MB for
> >capacity (close enough to 400MB) but I never seem to get close to
> >streaming:
> >
> >bs=     speed=
> >32k     50482 kps
> >128k    50531 kps
> >256k    50508 kps
> >512k    50521 kps
> >1024k   50512 kps
> >2048k   15780 kps
> >4096k   15875 kps
> >
> >Any hint on what I should try next?
> 
> Interesting.  What if you try with dd or tar rather than amtapetype?  On 
> my LTO3 drives testing with tar bs=32k yielded 41MiB/s while bs=2048k 
> yielded 60MiB/s.

That's what you were mentionning in a post last summer iirc.

One test just completed: here's what I get on a non-compression tape device

dd if=/dev/zero of=/dev/nst0 bs=32k
dd: writing `/dev/nst0': No space left on device
12424637+0 records in
12424636+0 records out
407130472448 bytes (407 GB) copied, 7000.04 seconds, 58.2 MB/s

Would you care posting the exact command that you used so that
we can really compare the numbers?

Some numbers I got from a local 1TB raidset (in a raid6 config)
to the tape drive:

tar -b 2048 -cf /dev/nst1 /export_raid04  (gives ~42MBs)
tar -b 4096 -cf /dev/nst0 /export_raid03  (gives ~42MBs)

so obviously the tapes went half-speed. 

I'm thinking of creating 2GB ramdisk, say, and filling it up with
random garbage and shoving that directly in the drive to get numbers
that bypasses the disks IO. I'll post them later.

> 
> Note also that LTO drives can throttle back to half of their native rate 
> (80MB/s for LTO3) without shoe-shining.

I'm aware of that fact. 
One of the main reason why I purchased LTO3 in fact!

thanks for the input.
regards, jf

> 
> -- 
> Joshua Baker-LePain
> Department of Biomedical Engineering
> Duke University

-- 
<° ><