Dan Dansereau wrote:
My apology for cross posting
We have a DELL6850 with 8Gbytes of memory, four 3.2Ghz CPU's , perc 4
raid controller, with fourteen 300Gbyte 10Krpm disk on a powervault
220s, And a powervault 124T LTO-3 tape systems on a separate
160Mbyte/sec adaptec SCSI card.
The disks are configured as two 2Tbyte raid 0 partitions using the perc
4 hardware.
The problem is - reading from the disk, and writing to the tape is
pathetically slow.
The specs say I should get around 80Mbyte/second - in reality - is about
500 Kbytes/second
Writing just to tape, using /dev/zero as input and dd to write, I can
get up to 60Mybte/second, indicating that the tape drive and scsi card
is functional from a hardware perspective. Since I can read and write
data to the disks - I assume that they are functional.
The files are 80Mybtes for the minimum size that I am writing to tape.
DELL Support hides behind the fact that CENTOS is not a supported OS,
But RED HAT is - so switch to it, so DELL can get RED HAT Support
involved. And the fact that Rocks is a modification to an unsupported
OS....
I have tried using various block size in tar from 256 to 8192 - with
minimal success.
Does anybody have any experience on setting the OS/Kernel parameters to
utilize the hardware at something more then a snails pace?
Or
Suggestions on what I could test and/or try?
I don't know anything about this specific hardware, but the usual
problem with tape is that if you can't feed it fast enough to stream at
its native speed it has to constantly stop, back up, and restart to
write the next chunk. Single-threaded programs normally can't because
they wait for a read to complete before starting the write. There are
programs around like mbuffer that allow the reading and writing to
overlap and provide a large buffer to minimize the restarts even if the
average throughput is still too slow.
Tapes also have a 'block size' that you can set with mt, and some
particular size may provide the best speed. With some drives, the write
block size from tar or obs= in dd must exactly match the tape block size
or be exact multiples.
--
Les Mikesell
lesmikesell@xxxxxxxxx
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