[OpenAFS] calculating memory
Fri, 28 Jan 2011 23:24:01 +0000
On 28 Jan 2011, at 20:24, Gary Gatling wrote:
> I am in charge of several afs servers in our college. Right now
> there are 5 afs servers running on 5 SPARC based servers. We are
> ditching Solaris since it sucks so bad and are going to move to
> Linux VM's running inside of VMware.
Firstly, I would be cautious about running I/O intensive services like
fileservers within a VM. You'll almost certainly get better
performance from bare metal, especially if you end up sharing the same
physical hardware between multiple fileservers.
> I was asked how much disk and memory we would need for the VMs. I
> was then critized for suggesting that each VM needs 4GB just like
> the real servers. I did not suggest the 4GB in each server. That was
> decided by a guy who quit a few years ago.
So, there are two separate considerations here. The first is making
sure that the processes on the machine have sufficient memory. The key
thing here is tuning your fileserver to suit its workload, and making
sure that you have enough callbacks to handle your number of clients.
You should be able to take a look at your existing servers, and see
how much memory the fileserver processes on them are consuming, and
use this as a rough guide. You definitely want to be in a position
where there is no way that your fileservers end up swapping.
The second consideration is page cache. Linux uses all of the "spare"
memory on a machine as a backing cache for the disk. Depending on the
working set of your fileservers, this can have significant performance
benefits. Without doing any analysis, it's hard to say how much memory
is necessary here, but in general, the more memory you can have as
cache, the better.
I don't think that 4G of memory of each of your 5 fileservers sounds
Hope that helps,