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03-25-2011, 04:59 PM #1Junior Guru Wannabe
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How to asses need for a server spec
I know there is the favourite pastime of buying what you can afford but is the re a magic formula of sites/users to RAM and CPU speed ..
I have a dedicated server that is only hosting 20 or so sites but several are forums and currently mysql is using around 25% of the cpu on its own.. Just upgrading to a better processor on the server seems a little of an intangeable thing of what to move to..
maybe I should get the forums on a 1 forum to 1 VPS deal but anyoone have a decent guide to max forum users to cpu core/ram rule of thumb guide ?
thanks
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03-25-2011, 06:22 PM #2
If you can get a graph of your cpu use and memory use, and disk i/o, then you can get a better idea for it. For sites that have a very predictable day-to-day load level, I try to keep the cpu use to 3/4 or below. For sites where usage is less predictable, 50% or less is preferable.
If you need to know, what kind of cpu will give you what kind of performance compared to your current server, that's certainly something we can help with, if you can give the specs of your current server, we could give an estimate of the cpu improvement by going to other specific processors.
It's also worth keeping in mind that the bottleneck is not always in the cpu. If you run out of memory, that can happen and be a huge problem, although you can often optimize memory use. Also, mysql databases are often very heavy on disk i/o, so you need to make sure i/o wait isn't causing the majority of your cpu use, otherwise a cpu upgrade would be pointless.
If your cpu use during peak times is under 50% of what your system is capable of, I wouldn't bother upgrading unless you were planning to see a large increase in the traffic the server needs to handle.IOFLOOD.com -- We Love Servers
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03-25-2011, 07:54 PM #3Junior Guru Wannabe
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Well earlier today things got very slow on the sites .. one forum had around 2500 users on there ofr a start
I have been keeping an eye on things and most of the evening has had 30% cpu usage by mysql.. enough ram seems to be available..
The current server is an E6500 with 2gb ram ... I was wondering if to go with one of the deals for 2x2.6 opteron with 8gb ram ..
It just seems a little heavy handed to move a server with so few sites but I have to assume its the CPU load that is causing the issues..
At one point today when it was real bad whm was showing nice little red cpu icon and something like 10.3 ... all evening its been poping from green to red in whm and hitting 2.0..
I just thought there must be a genius formula for such things rather than .. suck it and see
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03-25-2011, 09:16 PM #4Disabled
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you should make sure your mysql databases are optimized, also check your mysql server status with mysqltuner ,
can you provide some logs about I/O / ram usage / cpu usage over time?
sar command line tool can do that for you, on centos it's in the sysstat package from yum.
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03-25-2011, 10:15 PM #5
You certainly don't need to just blindly upgrade things, but without some historical information on what load the server is on, it is the best you can do. During peak loads, can you run "iostat -x 5 5" and wait about 30 seconds for it to complete. In the far right column, you'll see the utilization % of your disk drives. If this is above 50%, you'll be having an i/o wait issue.
Looking at top, what idle% cpu do you see during peak times? If it's less than 25%, then you would benefit from a faster cpu.
Also, how big are your databases? (du -cksh /var/lib/mysql to find the answer) If they don't entirely fit in ram, this can slow things down.
what do you get with "free -m"? You should see memory total, memory "used", memory free, memory for caching, and memory for buffers. Take the amount listed as being for caching, add it to the amount that's listed as free, and that's your true free memory. If this amount is less than the size of your databases, performance could be improved with more memory.
Also, how is your /etc/my.cnf file configured? By default, mysql won't even use the query cache, so you need to make some changes here if the file is mostly empty, or you'll have poor mysql performance.
You don't necessarily need to upgrade your server, but even if you do need it, without taking steps to see where your bottleneck is, you're just stabbing around blindly in the dark.IOFLOOD.com -- We Love Servers
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03-26-2011, 06:31 AM #6Junior Guru Wannabe
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As the old saying goes "Aye theres the rub " ..
To a degree I have bitten a little larger piece of pie than I probably should have .. but once your mouth is full you have to do something about it
I guess I really dont know enough Linux in the first place
It certainly seems a little strange (to me) that only 3 sites on a server hit it so much that it crawls at times .. it certainly make me wonder what hardware WHT have to ru to keep all the users on here happy
I will go dig round the server and see what I can find out ..
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03-26-2011, 07:43 AM #7Web Hosting Master
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03-26-2011, 11:44 AM #8
I would disagree. The default setting for keepalives is 5 or 15 seconds, which will use up all your apache slots, and make the site appear to be very sluggish, even if there is spare processing power. The first thing I do to any server is change the keepalivetimeout to 1 second. You'd be surprised how many times this will solve a server's performance problems without making any other changes at all.
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03-26-2011, 12:11 PM #9Web Hosting Master
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03-26-2011, 01:51 PM #10Junior Guru Wannabe
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Well after purchasing an expensive pile of magazines on server admin and linux .. the kind of thing that should be read *before* ending up at the sharp end of the server in the first place..
I found a more amicable solution .. use someone elses very much more experienced thumb.. pay them to check everything out and fix anything nasty before hopping onto a new flashy server that would end up with the same idiot in charge
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