Re: md RAID over SATA performance

["J.A. Magallon" <jamagallon@able.es>]

On 2004.09.03, 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:
> 
>

Thanks to everybody for its answers...

My confusion/problem was that I has always tried with only two drives,
and with more or less old drives that gave around 20-25Mb/s each, so
the raid worked very optimally at about 50 Mb/s.
But with modern drives at 55 Mb/s, I hit the PCI speed limits, I suppose.
Board is a Supermicro P3TDDE, Via ApolloPro 266T chipset (aghhh),
33 MHz PCI, 2xPIII@933.

With a stock 2.6.8.1, I get this:

nada:~# hdparm -tT /dev/md0

/dev/md0:
 Timing buffer-cache reads:   864 MB in  2.00 seconds = 431.63 MB/sec
 Timing buffered disk reads:  252 MB in  3.01 seconds =  83.85 MB/sec

with this setup:

nada:~# mdadm --detail /dev/md0
/dev/md0:
        Version : 00.90.01
  Creation Time : Fri Sep  3 02:17:28 2004
     Raid Level : raid5
     Array Size : 1225557760 (1168.78 GiB 1254.97 GB)
    Device Size : 245111552 (233.76 GiB 250.99 GB)
   Raid Devices : 6
  Total Devices : 6
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Fri Sep  3 19:01:39 2004
          State : clean
 Active Devices : 6
Working Devices : 6
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 256K

           UUID : fd6fcad0:21da140b:072a82b1:11b3db21
         Events : 0.239

    Number   Major   Minor   RaidDevice State
       0       8        1        0      active sync   /dev/sda1
       1       8       17        1      active sync   /dev/sdb1
       2       8       33        2      active sync   /dev/sdc1
       3       8       49        3      active sync   /dev/sdd1
       4       8       65        4      active sync   /dev/sde1
       5       8       81        5      active sync   /dev/sdf1


--
J.A. Magallon <jamagallon()able!es>     \               Software is like sex:
werewolf!able!es                         \         It's better when it's free
Mandrakelinux release 10.1 (RC 1) for i586
Linux 2.6.8.1-mm4 (gcc 3.4.1 (Mandrakelinux (Alpha 3.4.1-3mdk)) #8