Really high disk IO
I've got two different Linodes, and each one is hosting a website with similar traffic in pageviews and unique visitors: around 400K visitors/month and around 800k pageviews/month.
Those sites perform well, but there's a big difference in them: the disk IO usage. One of the sites has minimal disk IO, and the other one is using lots of disk IO, and I'm getting email alerts all the time (I've set the limit for emails high, but even with that I keep on receiving several emails per day).
The servers are running quite similar things: Both are Ubuntu 10.04 LTS machines, with Nginx web server, PHP-FPM, MySQL and a WordPress blog on each of them.
So I don't know what's the big difference that makes one so different from the other in terms of disk IO consumption.
Can I know which is the cause? How? What should I look for in logs, if I have to look those? What services can be really consuming? Could it be some wordpress plugin? I doubt this, because the config is quite similar between the two…
I attach a couple of images on which you can see the difference in IO Rate. Look at max, min and avg. Nonsense
Server 1: good
Server 2: baaad
8 Replies
If I was to hazard a guess I'd say either
1) You're swapping a lot
or
2) Your mysql settings need tweaking
install iotop (apt-get install iotop) and run
iotop -ao for say 10 minutes then paste the output here.
Could you post a screenshot of vmstat 5 (wait for the latter to print a dozen lines or so) on the "baaad" box?
iotop-ml (good):
iotop-mc (baaad):
vmstat (baaad):
I hope that helps!
iotop-ml (good):
iotop-mc (baaad):
vmstat (baaad):
I hope that helps!
I assume the iotops are are from around the same length of time, the good box has done..well pretty much nothing. The second one you have two processes that have done data writing/reading in the MBs, one is an nginx worker and the other is kjournald which is part of the ext3 journaling.
To be honest it looks like the bad one is receiving traffic and the good one isn't, are you serving up large image files/video files on the bad one?
Also what's the content of your /etc/fstab on the bad one.
The good:
the baaad:
There are more images on MuyComputer (the bad one), but we don't serve videos or heavy downloads, so I guess there's just a bad theming there or bad images managing on the WordPress' theme. But I'm not sure.
How can I know mysql is not doing something wrong? There's a cache on mysql, but maybe it's not well optimized…