Hi Nathan,
On Sun, Mar 23, 2008 at 01:51:04PM -0700, Tom Brown wrote:
> On Sun, 23 Mar 2008, n8&abby wrote:
>
> >I have between 35 and 40 domU's on the same box running the same
> >applications and each requiring moderate load. Each have between 150
> >to 512 megs of ram and 50Gb disk space. These domU's have really
> >become sluggish, even adding a large amount of memory helps only a
> >small amount. This may be normal for a system with this many domU's,
> >but I'm not really sure how to tell.
> >
> >Hardware is:
> >1U Acme 5CD16T Xeon 3000/3200 Core 2 Quad
> >4x SATA Drives (domU's are set up with LVM)
> >Intel Core 2 Quad Q6600 Quad-Core 2.40GHz 8MB
> >8Gb Ram
>
> So you've got 4 disk drives handling 40 different domUs... that's very
> likely to be your bottle neck, either that or flat out CPU power. If disk
> is your bottleneck, you want to try to find the domUs doing the most disk
> I/O and fix that... or give them more memory if they are doing substantial
> read I/O that might be cacheable. And if you build another server this way
> you might want to buy the fastest drives you can get/afford.
As Tom says, I would not be trying to run 40 virtual machines from 4
disk spindles, let alone 100, unless I *knew* they were all
CPU-limited (which would be a very unusual profile for the average
server).
If you want to put 100 general purpose servers on 1 piece of
hardware I suggest you look into a lot more than 4 disks, and
probably look at 10kRPM 2.5" SAS as well, as opposed to what I am
guessing are commodity 7200RPM 3.5" SATA disks.
Check the iowait % in your domains and dom0 - if it is more than a
few percent then it's IO you are needing i.e. more disks. I always
run out of IO before CPU or RAM too, it's pretty common.
Cheers,
Andy
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