schrieb Adrian Reyer am 10.07.2011 14:43 (localtime):
> Hi Harry,
>
> On Sun, Jul 10, 2011 at 01:38:52PM +0200, Harald Schmalzbauer wrote:
>> of a average transfer rate of 65MB/s makes me worrying about massive
>> repositioning.
>
> AFAIK LTO-Drives have adaptive speeds compared to older technologies. If
> the data comes in slower, the drive will just run slower on a somewhat
> constant speed. No more stop-and-go.
Hi Adrian,
thanks for your reply. I read about throttling capability, but `mt
status` shows drive state "at rest" even during active transferes.
The server is at remote site, so I can't hear any mechanicals, but I
guess "at rest" means stop, thus my worries about extensive repositioning.
>> Can I optimize my setup so that there won't be so many new files written
>> on tape? Or should the creation of a new file mark been done without
>> interruption of the transfer, and there's something wrong with my setup?
>
> Do you use 'Spool Data = yes'?
> To my understanding you can run multiple jobs to storage the same time,
> but they end up interleaved. Spooling the data will write full jobs or
> at least bigger chunks of a job in one run.
I have no backup jobs using the tape drive, so no spool is in use. I
only use the tape drive for migration (or sometimes copy) jobs. And in
the disk-pool I use "Use Volume Once = yes", so every job has it's own
file without interleaved data, which has exactly the size the job
summary reports.
Do you know if marking a "new file" on tape interrupts the LTO drive
from streaming? Perhaps it shouldn't interrupt streaming, and writing
many files for one job is a well choosen design, and I'm suffering from
some other misconfiguration which leads to interruption on marking new file.
If it's technically not possible to keep the drive streaming while
marking a new file, then I'm interested in tweaks how to avoid hundreds
of "new file" marks per backup job.
Do others see 208 files after 200G writte on tape?
Wild guess: If one file is marked every 1GByte written (wich takes max
12.8sec in my case), and this file mark interrupts the drive for round
about 4 seconds, then my transfer rate decreases from the usual rate for
uncompressable material of 80MB/s by 25% to ~60MB/s. That would exactly
represent the numbers I'm seeing here...
Which means the drive is only streaming 75% of the time, the rest is
used for repositionings :-(
Maybe this was not an issue with slower tape drives. LTO2 would only
suffer from about 6% performance loss, if my wild guess has any truth...
Thanks,
-Harry
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