And what about a raw disk tape to raw tape copy ?

# dd if=/dev/sda of=/dev/nst0 bs=32k count=32768

PS: 14 disk in raid 0 is very fragile, this should be used only for caching data. With a PV220 maybe a backup engine then !

On 9/2/07, Dan Dansereau ddansereau@hydropoint.com 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? Or Is there a standard disk / tape IO test package that could test the speed/performance of the disks and /or tapes?

Thanks for your help Dan A. Dansereau _______________________________________________ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos

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.

On Sun, 2 Sep 2007 at 8:11am, Dan Dansereau wrote

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.

Which card and driver? ISTR folks having issues with adaptec cards and LTO3 drives. Might you have a spare LSI SCSI card (ultra320, preferably) about that you could test with?

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

Have you benchmarked the disks to make sure you get decent performance out of them?

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.

80MB total or lots of 80MB files? If the former, you really need to test with, IMO, at least 2X RAM (preferably 4X) sized data to get a reliable speed estimate.

Is there a standard disk / tape IO test package that could test the speed/performance of the disks and /or tapes?

bonnie++ is somewhat standard for testing disk sequential read/write speeds.