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it's normal for you?

letboxletbox Member, Patron Provider
edited March 2013 in General

hay!
i'm doing some test at free server.
[root@xxx ~]# dd if=/dev/zero of=test bs=16k count=16k conv=fdatasync 16384+0 records in 16384+0 records out 268435456 bytes (268 MB) copied, 0.220392 s, 1.2 GB/s

1gb file

[root@xxxx ~]# dd if=/dev/zero of=test bs=64k count=16k conv=fdatasync 16384+0 records in 16384+0 records out 1073741824 bytes (1.1 GB) copied, 5.42847 s, 198 MB/s

Comments

  • seriesnseriesn Member
    edited March 2013

    Different stripe size? Less/smaller read and write? Perfectly fine. 1mb will write and read faster than 100mb ;)

  • IshaqIshaq Member
    edited March 2013

    One is bs=16k one is bs=64k.

  • letboxletbox Member, Patron Provider

    @Ishaq said: One is bs=16k one is bs=64k.

    expect this test from Raid10 SSD?

    The strip size 64K, i used 256K but slow like hell

  • rds100rds100 Member

    It's normal. Imagine a RAID card with 512MB of RAM buffer. The first test is 256MB and goes entirely in the RAID card's buffer (so is very fast). The second test is larger than the RAID card's buffer so must write to the disks and is thus slower.

  • letboxletbox Member, Patron Provider
    edited March 2013

    @rds100 said: It's normal. Imagine a RAID card with 512MB of RAM buffer. The first test is 256MB and goes entirely in the RAID card's buffer (so is very fast). The second test is larger than the RAID card's buffer so must write to the disks and is thus slower.

    Same Raid setting

    [root@xxx ~]# dd if=/dev/zero of=test bs=64k count=16k conv=fdatasync
    16384+0 records in
    16384+0 records out
    1073741824 bytes (1.1 GB) copied, 1.41293 s, 760 MB/s

    then it go slow like hell.

  • rds100rds100 Member

    Yes, first time you filled the buffer of the RAID card, then it slowly starts to write it to the disks. You start another test, there is no free space in the buffer yet, you should wait.
    Do the same test twice with 1 second interval between the two -> the second will be slow.
    Do the tests again with 20-30 second interval between the two -> the second will be fast.

  • letboxletbox Member, Patron Provider

    @rds100 said: Yes, first time you filled the buffer of the RAID card, then it slowly starts to write it to the disks. You start another test, there is no free space in the buffer yet, you should wait.

    Do the same test twice with 1 second interval between the two -> the second will be slow.
    Do the tests again with 20-30 second interval between the two -> the second will be fast.

    The second test done on the Server then reinstalled and get the slow test :)

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