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Thread: %iowait VPS question
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05-08-2011, 04:57 PM #1Junior Guru Wannabe
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%iowait VPS question
In the last few weeks I have been having a lot issues with timeouts on a Joomla website (120seconds, which is the default for IPCConnectTimeout / fcgid). The website on that server has roughly 200 visitors per day.
I checked the load with sysstat / sar and noticed that for quite some a few hours per day the %iowait hovers around 60 to 80 (average per day is roughly 8).
My question: Is there anything I can tune on my VPS (Centos 5.6) to deal with this situation? I don't think that increasing the timeout to 10 minutes would help, because users wouldn't wait that long anyway.
Thanks for any ideas in advance!
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05-08-2011, 05:02 PM #2Retired Moderator
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200 visitors per day total? That isn't much at all. Are you out of memory?
It's possible that your VPS node is being overloaded by other customers. May be worth contacting your host about the iowait.
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05-08-2011, 05:12 PM #3Junior Guru Wannabe
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I have 2GB (4GB burstable) memory (typlically memory usage is 1GB or less). I contacted the host (of course) already quite a while ago, but believe this situation could last for a "longer period. So I am checking what I could do on my end to deal with this situation.
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05-08-2011, 05:16 PM #4Retired Moderator
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What processes are showing up with the following command during high iowait?
watch -n 1 "(ps aux | awk '\$8 ~ /D/ { print \$0 }')"
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05-08-2011, 05:22 PM #5Junior Guru Wannabe
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Are you running any exotic plugins for your joomla site that could create issues? If not I would say that you don't get what you pay for. Make this clear to your host. If things don't change soon, give to another host your money. 200 visitors/day is nothing, so you should have no issues at all even with a non optimized vps.
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05-08-2011, 05:30 PM #6Junior Guru Wannabe
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05-08-2011, 05:36 PM #7Junior Guru Wannabe
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05-08-2011, 06:24 PM #8Junior Guru
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iowait is usually storage congestion
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05-09-2011, 02:21 PM #9Junior Guru Wannabe
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Still waiting to try:
Code:watch -n 1 "(ps aux | awk '\$8 ~ /D/ { print \$0 }')"
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05-09-2011, 02:55 PM #10ShillBuster
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One Joomla site? I'm running 90 of them on my 1GB KnownHost VPS and it never misses a beat.
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05-09-2011, 03:09 PM #11Junior Guru Wannabe
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Yes, I know, my VPS is very inexpensive compared to knownhost. I guess you get what you pay for - sometimes :-)
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05-10-2011, 03:33 PM #12Junior Guru Wannabe
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Ok, today the iowait was horrible again, but I was able to try the command.
Code:watch -n 1 "(ps aux | awk '\$8 ~ /D/ { print \$0 }')"
The %iowait is around 70. The problem typically starts at every full hour and stops after 10-20 minutes (or even longer on very bad days). It looks like some scheduled jobs cause this (none of my jobs apparently).
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05-10-2011, 03:37 PM #13Retired Moderator
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05-10-2011, 03:52 PM #14Junior Guru Wannabe
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Ok, understand.
The host has been "investigating" for a few weeks already ... So hopefully they are able fix the problem (once they actually moved my OpenVZ container to a different node, but it didn't help).
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05-11-2011, 05:43 AM #15
It sounds like they're just piling on a ton of customers onto nodes that aren't powerful enough to handle the customers on them. A couple hundred visitors a day isn't enough for your usage to be causing any problems. The only other potential cause is that a couple abusive users on the node are using up all the disk i/o, but if that were the case, the host should resolve that by suspending the abusive users. The fact that the problem persists certainly is a case of you get what you pay for: if the host were on the ball, they'd either have servers that were powerful enough to handle their customers, or they would investigate and suspend abusive customers (depending on the situation).
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05-11-2011, 12:58 PM #16Web Hosting Master
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I bet you could throw the site on a ramdisk if you wanted a quick fix. If they're overselling they may not be thrilled by it, but you do what you gotta do
Ain't here to spam my signature, I'm not desperate for sales.
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05-11-2011, 01:12 PM #17Web Hosting Evangelist
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Who is your VPS provider? Do you know what drives are they using? Any RAID?
You can test the I/O using the following command:
dd if=/dev/zero of=test bs=64k count=16k conv=fdatasync
Please share the output with us so we can tell you if it's acceptable.██ KnownSRV.com - Privacy. Managed. Secure. Guaranteed!
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05-11-2011, 03:24 PM #18Junior Guru Wannabe
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05-11-2011, 03:55 PM #19Junior Guru Wannabe
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I don't want to name the provider in this thread. I am just trying to figure out some options how to deal with the situation. I never expected high performance and 99% availability from them. Just a good compromise between price and performance. It had worked until april ...
I believe they mentioned Raid 10 once.
And here is the result for your test:
Code:[root ~]# dd if=/dev/zero of=test bs=64k count=16k conv=fdatasync 16384+0 records in 16384+0 records out 1073741824 bytes (1.1 GB) copied, 111.718 seconds, 9.6 MB/s
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05-11-2011, 05:30 PM #20Web Hosting Evangelist
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Ouch, it's TERRIBLE. I'd ask them to migrate you to some other VPS Node, if they have any Node that is NOT overloaded like your current one(from the looks off your output).
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05-11-2011, 05:43 PM #21Junior Guru Wannabe
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Thanks for the feedback. What value would be acceptable?
I asked them to move my container again, but they rejected this. They said this would have a significant negative impact on the iowait. Not sure whether I should push for this (because the other nodes had similiar issues before).
I should probably try the RAM disk, my site is very small (20MB).
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05-11-2011, 06:46 PM #22WHT Addict
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I don't want to name the provider in this thread
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05-11-2011, 06:47 PM #23Disabled
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05-11-2011, 08:58 PM #24Poooooonnyyy :*
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I should add that ramdisks are a scary thing if your node reboots you'll lose the data that was in there requiring you to refill it.
You could probably have any sort of caching folders go there to help some but even then most decent webservers will cache to memory some at least anyways.
Francisco
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05-11-2011, 09:39 PM #25WHT Addict
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it looks the node is oversold. contact you host to move to another node or switch the host.
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