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SubjectPoor SATA / RAID performance (2.6.11 and promise SATAII150 TX4)
Greetings,

I'm attempting to benchmark software RAID5 on a system with:
- Promise SATAII150 TX4 card
- 4 Segate ST3300831AS drives
- custom built kernel 2.6.11 (to get driver for promise SATAIITX4)
- FC3 install
- EPIA M10000 mainboard, 256MB memory

The tools I'm familiar with for benchmarking a PATA based RAID system are:
- hdparm
- dd

Here are some interesting stats from my system:

[root@epiam10k ~]# more /proc/mdstat
Personalities : [raid5]
md0 : active raid5 sdd1[3] sdc1[2] sdb1[1] sda1[0]
879100608 blocks level 5, 4k chunk, algorithm 2 [4/4] [UUUU]

unused devices: <none>
[root@epiam10k ~]# hdparm -t /dev/sda

/dev/sda:
Timing buffered disk reads: 116 MB in 3.02 seconds = 38.45 MB/sec
HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate ioctl for
device
[root@epiam10k ~]# hdparm -t /dev/sda1

/dev/sda1:
Timing buffered disk reads: 104 MB in 3.05 seconds = 34.10 MB/sec
HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate ioctl for
device
[root@epiam10k ~]# hdparm -t /dev/md0

/dev/md0:
Timing buffered disk reads: 72 MB in 3.03 seconds = 23.79 MB/sec

[root@epiam10k ~]# vmstat
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
1 0 0 3628 8984 142704 0 0 423 23 1023 112 30 3 61 6

Observations:
- the performance of a raw SATA device (/dev/sda in the above example) seems
low when I compare it to a PATA drive from a previous system (which would get
about 45MB/sec)
- the performance of the RAID5 array (/dev/md0) seems very low - I expect
quite an increase over a single device due to striping
- the number of interrupts per second (1023) seems very high

Questions:
- is hdparm the right tool for looking at SATA devices?
- is the error regarding the ioctl an issue?
- how do I set/get the DMA modes for the SATA controller and SATA drives?
- why would the interrupts per sec reported from vmstat be so high?

Thanks for any suggesitons. Please 'cc' me in any replies to the list.

Tim Harvey
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