Date: Mon, 5 Mar 2001 17:02:15 -0800 (PST) From: Matt Dillon <dillon@earth.backplane.com> To: Dan Phoenix <dphoenix@bravenet.com> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: systat -vmstat or iostat IO help Message-ID: <200103060102.f2612FH47843@earth.backplane.com> References: <Pine.BSO.4.21.0103051634080.6833-100000@gandalf.bravenet.com>
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:this is a webserver ......i am trying to figure out if cpu increase or
:scsi drives is better in this situation. Right now...that is a big
:decision because there are approx 30 fbsd webservers ....not all showing
:high IO from vmstat...just the ones with the highest uptime.
:...
Check the memory load with 'systat -vm 1'... if you are swapping a
lot simply adding more memory may solve the problem. Generally speaking,
adding more memory to a web server helps a lot even if you aren't
swapping because web servers tend to be heavy on reading files.
Today's machines are powerful enough that you can serve thousands of
users off a single host, but drive technology isn't powerful enough to
serve large datasets off a single drive so you need a lot of ram for
cache. For example, a 20G hard drive may be able to store 20G worth
of files, but it sure won't be able to keep up with a heavily loaded
webserver unless you have a lot of ram for caching. Drive seek times
tend to top out at 6ms, or 166 seeks per second, and without sufficient
memory to cache the web pages this will result in severe limitations
to the number of hits/sec the webserver can handle.
-Matt
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