sata promise and software raid5...

[Andrey Nekrasov]

Hello,

controller - Promise SATA 150 TX4, linux 2.6.7-rc1-bk1, HDD Maxtor
250Gb (x4)

Why so slowly reads (and writes) with software raid5?

gnome:~ # hdparm -t /dev/sda2

/dev/sda2:
 Timing buffered disk reads:  148 MB in  3.01 seconds =  49.16 MB/sec
gnome:~ # hdparm -t /dev/sdb2

/dev/sdb2:
 Timing buffered disk reads:  148 MB in  3.02 seconds =  49.01 MB/sec
gnome:~ # hdparm -t /dev/sdc2

/dev/sdc2:
 Timing buffered disk reads:  148 MB in  3.03 seconds =  48.90 MB/sec
gnome:~ # hdparm -t /dev/sdd2

/dev/sdd2:
 Timing buffered disk reads:  144 MB in  3.00 seconds =  47.96 MB/sec
gnome:~ #
gnome:~ #
gnome:~ # hdparm -t /dev/md0

/dev/md0:
 Timing buffered disk reads:   64 MB in  3.12 seconds =  20.52 MB/sec
gnome:~ #


gnome:~ # cat /etc/raidtab
raiddev /dev/md0
        raid-level              5
        nr-raid-disks           4
        nr-spare-disks          0
        persistent-superblock   1
        parity-algorithm        left-symmetric
        chunk-size              1024

        device                  /dev/sda2
        raid-disk               0

        device                  /dev/sdb2
        raid-disk               1

        device                  /dev/sdc2
        raid-disk               2

        device                  /dev/sdd2
        raid-disk               3

        
bye
--


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