Re: md RAID over SATA performance

[Brad Campbell]

J.A. Magallon wrote:
> Hi all...
>
> I am buildin an array with a linux box, and I run 2.6.8.1 (not stock, but
> the mandrake cooker version).
>
> Disks are 6 SATA drives, plugged to a couple of Promise FastTrak S150 TX4
> cards.
>
> Problem is that i get really poor performance. A single drive gives about
> 57 Mb/s, and a raid1 with two just gives about 64 Mb/s (measured with
> hdparm -tT). With the six drives:
>
> nada:~/soft/kernel# hdparm -tT /dev/sda
>
> /dev/sda:
> Timing buffer-cache reads:   844 MB in  2.01 seconds = 419.96 MB/sec
> Timing buffered disk reads:  174 MB in  3.01 seconds =  57.84 MB/sec
> nada:~/soft/kernel# hdparm -tT /dev/md0
>
> /dev/md0:
> Timing buffer-cache reads:   884 MB in  2.00 seconds = 441.63 MB/sec
> Timing buffered disk reads:  310 MB in  3.01 seconds = 103.07 MB/sec
>
> The real goal is to build a raid5 system, but I just tested with raid1.

Here are some real-world figures for you (Not that they mean anything!)

srv:/home/brad# hdparm -t -T /dev/md0

/dev/md0:
 Timing buffer-cache reads:   1340 MB in  2.00 seconds = 668.76 MB/sec
 BLKGETSIZE failed: File too large
 Timing buffered disk reads:  182 MB in  3.02 seconds =  60.31 MB/sec
srv:/home/brad# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/hda1              19G   11G  6.5G  64% /
tmpfs                 252M     0  252M   0% /dev/shm
/dev/hda3             165G   21G  136G  13% /raid0
/dev/md0              2.1T  2.0T  114G  95% /raid
/dev/md2              459G  101G  358G  22% /raid2
srv:/home/brad# mdadm --detail /dev/md0
/dev/md0:
        Version : 00.90.01
  Creation Time : Sun May  2 18:02:14 2004
     Raid Level : raid5
     Array Size : 2206003968 (2103.81 GiB 2258.95 GB)
    Device Size : 245111552 (233.76 GiB 250.99 GB)
   Raid Devices : 10
  Total Devices : 10
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Fri Sep  3 16:08:03 2004
          State : clean, no-errors
 Active Devices : 10
Working Devices : 10
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-asymmetric
     Chunk Size : 128K

    Number   Major   Minor   RaidDevice State
       0       8        1        0      active sync   /dev/devfs/scsi/host0/bus0/target0/lun0/part1
       1       8       17        1      active sync   /dev/devfs/scsi/host1/bus0/target0/lun0/part1
       2       8       33        2      active sync   /dev/devfs/scsi/host2/bus0/target0/lun0/part1
       3       8       49        3      active sync   /dev/devfs/scsi/host3/bus0/target0/lun0/part1
       4       8       65        4      active sync   /dev/devfs/scsi/host4/bus0/target0/lun0/part1
       5       8       81        5      active sync   /dev/devfs/scsi/host5/bus0/target0/lun0/part1
       6       8       97        6      active sync   /dev/devfs/scsi/host6/bus0/target0/lun0/part1
       7       8      113        7      active sync   /dev/devfs/scsi/host7/bus0/target0/lun0/part1
       8       8      129        8      active sync   /dev/sdi1
       9       8      145        9      active sync   /dev/sdj1
           UUID : 05cc3f43:de1ecfa4:83a51293:78015f1e
         Events : 0.681631
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