Rudolf Cejka wrote:
Keith Brautigam wrote (2006/02/16):
What actual speed are you getting now during the de-spooling process?
Typically 60 - 80 MB/s (note that file boundaries on tapes temporarily
slows down the speed), however now my backup is idle, so I could not
see it right now.
Also, how would you recommend measuring how fast you are writing to the
tape (I realize you're on FreeBSD not Linux)? I'm new to having such a
fast drive and am also interested in in creasing write performance.
On FreeBSD, I do use personally modified iostat with possibility to print
timestamps for long offline monitoring, or standard iostat 1 or iostat [2345]
output for online monitoring. On Linux, maybe I would try to use
iostat -m 5 for offline monitoring and iostat -m 1 or iostat -m [23] for
online monitoring..
How did you arrive at using hardware RAID and seven drives? Was that
It was one of our free video servers at a time ;o)
convenient with your hardware, or did you first try a smaller number of
drives (like I have) and find they were not enough?
Unfortunately I'm going in the reverse way - now I have to switch to another
machine and I'm currently trying two-core 3.2 GHz with 2 GB RAM, one disk for
MySQL and 2 or 3 disks for data spooling using software RAID0 (gstripe).
Then I will see, if it is or is not similar to the current state.
How do you find/set the number of repositions? What other sorts of
tuning did you perform on the drive?
Interesting performance logs from drives can be readed using LOG_SENSE or
MODE_SENSE SCSI commands. SCSI command reference for IBM LTO drives can
be downloaded freely from internet, but reference for HP LTO drives was
very hard to get for me (is there anybody with access to this type of
documentation? HP has several books to this topic and I'm happy that
I have personal access to atleast part 3 with SCSI command reference).
Other information can be readed directly from my scripts located in
ftp://ftp.cz.FreeBSD.org/pub/FreeBSD-local/scsi.
So it sounds like I should be okay with an older Adaptec 160 MB/s card?
Please no ;o) I'm still afraid, that I could not see any speed differences
because of another problem and would be happy to see experiences from the
others. Maybe the problem is in FreeBSD and Linux would perform better.
The problem is that I never seen value over 100 MB/s from iostat 1
output for any data even with good compression ratio, which looks
suspicious.
I use two patches for FreeBSD kernel:
- Standard FreeBSD allows just 128 KB max. physical request (disks and so
on), so I increase it to 384 KB (which is twice the size of max. allowed
physical request for my LSILogic 1030 Ultra4 320 MB/s.
- Standard FreeBSD allows just 64 KB max. physical request for SCSI tapes,
so I increase it to 192 KB, where ~ 196 KB/t seems to be limit of
LSILogic adapter card (Adaptec allows bigger physical blocks, however
again without performance differences for me :o/). However, if you switch
to another hardware/software, you can make your data unreadable: I had an
Adaptec with 256 KB/t and after switching to LSI 192 KB/t, I had to have
Adaptec still available, so that I would be ready to read data written
with 256 KB/t (all is meant SCSI physically - it is different thing
from OS layer, which can break down bigger requests to the smaller ones).
Regards.
Thank you very much for all of the information. The link to the HP
website was useful. I will checkout the SCSI logs you mentioned. If I
have an opportunity get a 320 card I will let you know the results under
Linux. First, I will re-test my disk IO performance as that seems the
most likely bottleneck.
Also, thank you for the iostat tips and for providing the links to your
SCSI scripts and the general background information on SCSI. I am
curious to know what your tape writing speed is on the new system that
has less disks for the spool (whenever you have that data). It's always
nice to have something to compare my performance to.
Regards
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