On 1/5/2010 5:44 PM, Matt wrote:
> I just installed CentOS 5.4 64 bit release on a 1.9ghz CPU with 8gB of
> RAM. It has 2 Western Digital 1.5TB SATA2 drives in RAID1.
>
> [root@server ~]# df -h
> Filesystem Size Used Avail Use% Mounted on
> /dev/md2 1.4T 1.4G 1.3T 1% /
> /dev/md0 99M 19M 76M 20% /boot
> tmpfs 4.0G 0 4.0G 0% /dev/shm
> [root@server ~]#
>
> Its barebones right now. Nothing really running. I intended to move
> our current email server over to it eventually. The thing is slow as
> mud due to disk I/O though. I have no idea whats going on.
>
> Here is a bit of iostat -x output.
>
> [root@server ~]# iostat -x
> Linux 2.6.18-164.9.1.el5 (server.x.us) 01/05/2010
>
> avg-cpu: %user %nice %system %iowait %steal %idle
> 0.13 0.10 0.03 38.23 0.00 61.51
>
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz
> avgqu-sz await svctm %util
> sda 0.18 0.33 0.04 0.20 27.77 4.22 132.30
> 3.70 15239.91 2560.21 61.91
> sda1 0.00 0.00 0.00 0.00 0.34 0.00 654.72
> 0.01 12358.84 3704.24 0.19
> sda2 0.18 0.00 0.04 0.00 27.30 0.00 742.93
> 0.30 8065.37 1930.35 7.09
> sda3 0.00 0.33 0.01 0.20 0.14 4.22 21.29
> 3.40 16537.41 3008.03 61.52
sda3 is running "hot" with a 62% utilization
> sdb 0.19 0.33 0.06 0.20 28.39 4.22 126.29
> 2.51 9676.49 862.49 22.27
> sdb1 0.00 0.00 0.00 0.00 0.34 0.00 606.29
> 0.00 2202.03 643.13 0.04
> sdb2 0.18 0.00 0.04 0.00 27.30 0.00 724.25
> 0.10 2579.45 745.76 2.81
> sdb3 0.01 0.33 0.02 0.20 0.75 4.22 22.61
> 2.41 10913.16 988.40 21.74
sdb3 is running at 22% utilization
> Does anyone have an idea what I have wrong here? This is my first
> software RAID install. Built a number of Centos servers without RAID
> and they have all worked fine.
>
As mentioned by others, atop & lsof are good for figuring out what is
touching the disk. Something writing to the disk (wsec/s) and doing it
fairly evenly while also reading from the 2nd partition.
You could try hdparm (hdparm -tT /dev/sda) and see what speeds you get
for the individual drives, then compare that to the speed you get off of
say /dev/md2. Or if you want a stronger load that lasts for a minute or
two, try using dd and dumping to /dev/null (dd if=/dev/sda of=/dev/null
bs=1M count=1000). The individual drive speeds should match up pretty
closely with the Software RAID speed.
A pair of 1.5GB 7200RPM SATA drives should be able to handle up to a few
hundred thousand to a million or so messages per month (Postfix /
Dovecot). As long as that's at least a dual-core 1.9GHz CPU. YMMV of
course and watching server performance over the long term will be your
best bet.
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