lkml.org 
[lkml]   [2003]   [Dec]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: raid0 slower than devices it is assembled of?
    On Mon, Dec 15, 2003 at 02:34:54PM +0100, Witold Krecicki wrote:
    > I've got / on linux-raid0 on 2.6.0-t11-cset-20031209_2107:
    > <cite>
    > /dev/md/1:
    > Version : 00.90.01
    > Creation Time : Thu Sep 11 22:04:54 2003
    > Raid Level : raid0
    > Array Size : 232315776 (221.55 GiB 237.89 GB)
    > Raid Devices : 2
    > Total Devices : 2
    > Preferred Minor : 1
    > Persistence : Superblock is persistent
    >
    > Update Time : Mon Dec 15 12:55:48 2003
    > State : clean, no-errors
    > Active Devices : 2
    > Working Devices : 2
    > Failed Devices : 0
    > Spare Devices : 0
    >
    > Chunk Size : 64K
    >
    [snip]

    > Disks are two ST3120026AS connected to sii3112a controller, driven by sata_sil
    > 'patched' so no limit for block size is applied (it's not needed for it).
    >
    > Those are results of hdparm -tT on drives:
    > <cite>
    > /dev/md/1:
    > Timing buffer-cache reads: 128 MB in 0.40 seconds =323.28 MB/sec
    > Timing buffered disk reads: 64 MB in 1.75 seconds = 36.47 MB/sec
    > /dev/sda:
    > Timing buffer-cache reads: 128 MB in 0.41 seconds =309.23 MB/sec
    > Timing buffered disk reads: 64 MB in 1.46 seconds = 43.87 MB/sec
    > /dev/sdb:
    > Timing buffer-cache reads: 128 MB in 0.41 seconds =315.32 MB/sec
    > Timing buffered disk reads: 64 MB in 1.23 seconds = 52.04 MB/sec
    > </cite>
    > What seems strange to me is that second drive is faster than first one
    > (devices are symmetrical, sd[a,b]2 is swapspace (not mounted at time of
    > test), sd[a,b]1 is /boot (raid1)).

    Possible reasons:

    internal differences on controller

    block remapping (even new disks have bad blocks)

    different firmware

    different physical geometry -- two production runs of
    the same make+model drive may have different
    geometry

    cable quality or routing differences, or interface
    variations that cause subtle timing differences


    > What is even stranger is that raid0 which should be faster than single drive,
    > is pretty much slower- what's the reason of that?

    You could try increasing the read ahead but that may slow
    things down in real world use.

    AID-0 isn't RAID (no R), but then again for many arrays the
    I is also out of place.

    --
    ________________________________________________________________
    J.W. Schultz Pegasystems Technologies
    email address: jw@pegasys.ws

    Remember Cernan and Schmitt
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-03-22 13:59    [W:0.027 / U:0.484 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site