[Beowulf] OT: LTO Ultrium (3) throughput?

[Vincent Diepeveen]

Hi Dave,

Probably the i/o is  your limiting factor.
Using raid10 or something?

Ignore that factor 2 compression by the way, that's just marketing  
paper.

My LTO-2 gets about 28MB/s uncompressed streamspeed, for compressed  
files
  (7-zip is far superior to anything else currently under linux).
Usually i also store longterm data with 10% par2 data
(free linux tool is there for it as well),  so that i can recover bit  
errors later on.

That 28MB/s is at least what i observe, could be tad optimistic :)

The initial problems i had also with streamspeed and also reading back
was all software based. A lot of backup software was real ugly bad  
simply.

What mattered at the raid10 array also was the file system used and how
far loaded it already was. Reading files from a raid10 is not  
necessarily fast.

Harddrives are relative fast when reading/writing blocks of 128-512KB  
or so,
whereas filesystems use far smaller blocksizes to store in reality.

Very bad to stream a couple of hundreds of GB to tape.

The software used is important. Default backup software was dubious  
in my case
and the biggest reason for problems. After that was fixed, the i/o  
speed is a problem
when storing tiny files at tape.

But well i'm a total layman with backups. Perhaps you already figured  
out your problem.

Vincent


On Jun 19, 2008, at 2:04 AM, David Mathog wrote:

> If any of you have an LTO Ultrium-3 drive what kind of speeds are you
> observing?  On one Linux system here (kernel 2.6.24-19) we have an
> HP Ultrium-3 attached to an Adaptec ASC-29320ALP U320 controller.
> There is nothing else on that SCSI bus, termination and cable seem  
> good.
> Getting into scsi-select from the BIOS shows everything set to 320.
> No error messages or warnings are appearing. Yet:
>
>   dd if=/dev/zero of=/dev/nst0 bs=8192 count=10000
>
> only moves 21.3MB/sec.  The HP documentation indicates 432GB/hour,
> (compressed) which is 120 Mb/sec, so we're off by 6X (or maybe 3X for
> 2:1 compression, either way, a lot).  The system's CPU and memory
> aren't rate limiting as
>
>   dd if=/dev/zero of=/dev/null bs=8192 count=10000
>
> moves 6.9GB/sec.
>
> Any thoughts where the bottleneck might be?
>
> Thanks,
>
> David Mathog
> mathog at caltech.edu
> Manager, Sequence Analysis Facility, Biology Division, Caltech
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