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.