the first write some dd more slowly (This RBD-test is based on other RBD)

Ta Ba Tuan <tuantb@xxxxxxxxxx> · Mon, 02 Nov 2015 10:15:10 +0700



    Hi everyone.

    
    Had a problem about speed write by some write frist dd(s) on my
    rootdisk (My rootdisk-RBD was based on other RBD-Image). It have run
    more slowly, but running faster after.

    (I used writeback cache on RBD Client side and RAID Phisycal).

    
    #dd if=/dev/zero of=bigfile01 bs=1M count=500 conv=fdatasync

    100+0 records in

    100+0 records out

    104857600 bytes (105 MB) copied, 5,51315 s, 19,0 MB/s

    
    Then:

    #dd if=/dev/zero of=bigfile03 bs=1M count=500 conv=fdatasync

    300+0 records in

    300+0 records out

    314572800 bytes (315 MB) copied, 4,16175 s, 75,6 MB/s

    
    Please explain this proplem to me!,

    Thanks!

    --

    Tuantaba

    Ha Noi-VietNam

    
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