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    SubjectRe: raid0 slower than devices it is assembled of?


    Size is MB, BlkSz is Bytes, Read, Write, and Seeks are MB/secd . -T

    File Block Num Seq Read Rand Read Seq Write Rand Write
    Dir Size Size Thr Rate (CPU%) Rate (CPU%) Rate (CPU%) Rate (CPU%)
    ------- ------ ------- --- ----------- ----------- ----------- -----------
    . 2018 4096 1 244.7 53.6% 8.847 2.26% 88.04 41.7% 5.594 7.16%
    . 2018 4096 2 281.6 65.6% 11.04 3.53% 89.86 69.5% 6.645 9.78%
    . 2018 4096 4 235.6 64.3% 13.91 4.45% 88.26 96.2% 7.647 12.7%
    . 2018 4096 8 231.2 68.0% 15.91 5.34% 85.59 105.% 7.557 10.3%

    Two channel, Six drives, three per channel.

    U320 with 15K U160 drives in a soft Raid 0.

    Andre Hedrick
    LAD Storage Consulting Group

    On Tue, 16 Dec 2003, Andre Hedrick wrote:

    >
    > Helge,
    >
    > Reads you may gain on writes only if all devices are on single ended mode.
    > Both pATA and pSCSI suck wind in writes, pSCSI should smoke pATA on reads.
    > It is all a matter of the physical protocol on the wire.
    >
    > Only in SATA/SAS will you even reach close to ideal world.
    >
    > Cheers,
    >
    > Andre Hedrick
    > LAD Storage Consulting Group
    >
    > On Tue, 16 Dec 2003, Helge Hafting wrote:
    >
    > > jw schultz wrote:
    > >
    > > > No Linux [R]AID improves sequential performance. How would
    > > > reading 65KB from two disks in alternation be faster than
    > > > reading continuously from one disk?
    > > >
    > > Raid-0 is ideally N times faster than a single disk, when
    > > you have N disks. Because you can read continuously from N
    > > disks instead of from 1, thereby N-doubling the bandwith.
    > >
    > > Wether the current drivers manages that is of course another story.
    > >
    > > Helge Hafting
    > >
    > >
    > > -
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