Hi. I''m planning to create a new Xen 3.1 installation, and I''m trying to think how many domUs I will be able to run on it. The server on which the dom0 will run will be this: - Dell PowerEdge SC1435 - 2 x Dual Core AMD Opteron 2212 2.0 GHz - 16 Gb RAM DDR2 667MHz - 2 x 320 Gb hard disk SATA2 Do you think it will be able to host 100~120 domUs of 128 Mb RAM? Thank you very much! Bye. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> > Definitely not. My first concern would be disk I/O contention. >How many domUs do you think that server will be able to support? _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Mon, 16 Jul 2007, shacky wrote:>> >> Definitely not. My first concern would be disk I/O contention. >> > How many domUs do you think that server will be able to support?It depends how much IO the domUs will generate. 2xSATA isn''t that fast... /Jonas _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> > It depends how much IO the domUs will generate. 2xSATA isn''t that fast...Couldn''t we estimate it? ~20, ~50, ~70? _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
What do you plan to use each domU for? 128MB isnt much at all. From: xen-users-bounces@lists.xensource.com [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of shacky Sent: Monday, July 16, 2007 5:16 PM To: Jonas Björklund; xen-users@lists.xensource.com Subject: Re: [Xen-users] dom0 performances It depends how much IO the domUs will generate. 2xSATA isn''t that fast... Couldn''t we estimate it? ~20, ~50, ~70? _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Mon, 16 Jul 2007, shacky wrote:>> >> It depends how much IO the domUs will generate. 2xSATA isn''t that fast... > > > Couldn''t we estimate it? ~20, ~50, ~70?70 random seeks per second should be reasonable (7200 rpm = 4ms average rotational latency, 8ms average seek time -> 12ms per random seek -> would suggest that 83 completely random I/O''s is achievable on a standard 7200rpm drive with 8ms seek times. However, that''s basically just another meaningless number.... It''s hard to have any real idea of how many I/O''s are random and how many are sequential. It''s also dramatically affected by how much memory each domU has for disk caching and of course, but what the domU workload is. Looking up keys in a 20 Meg mysql database is going to be completely cacheable. Full table scans (or even selecting a few thousand random rows) of a 10 or 100 gigabyte database will drive almost any I/O subsystem nuts (and if you have a massively parallel drive system, just keep adding clients, it is still overloadable). Logging data to a mysql table will be pretty much sequential writes and schedulable at the kernels convenience. Running a webserver to serve a couple meg of static files is completely cacheable. Running a LAMP setup on a domU that has only enough memory to actually load apache/mysql into memory is going to be hard on disk (because there won''t be any disk caching). And this IMHO is the biggest problem with virtual machine hosting. Accounts tend to be sized by memory, and the clients thus slot themselves into the smallest amount of memory they can survive in, and consequently burn out the disk subsystem... and AFAIK, xen (and probably most other virtual hosting solutions), do not have good control/scheduling/limiting of/over the amount of disk activity caused by a domU. Allocating a drive to each domU is wastefull, limiting, and counter to the goals of virtualization... but it does greatly reduce the effect of the domUs on each other. ---------------------------------------------------------------------- | How often I found where I should be going http://BareMetal.com/ | only by setting out for somewhere else. web hosting since ''95 | -- R. Buckminster Fuller _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> What do you plan to use each domU for? 128MB isn''t much at all. >I cannot know this precisely, because the VMs will be assigned to some customers... In particular, they will be most used for some LAMP installation, but customers will be able to do anything with them... _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
I''ve found that you can typically get 4-8 VMs per spindle. This assumption is entirely general and can entirely break down as there are plenty of examples of applications that could require dozens of spindles per VM! -- -- Tom Mornini -- Sent from my iPhone On Jul 16, 2007, at 2:15 PM, shacky <shacky83@gmail.com> wrote:> It depends how much IO the domUs will generate. 2xSATA isn''t that > fast... > > Couldn''t we estimate it? ~20, ~50, ~70? > _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-users_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
I''ve found that you can typically get 4-8 VMs per spindle. This assumption is entirely general and can entirely break down as there are plenty of examples of applications that could require dozens of spindles per VM! -- -- Tom Mornini -- Sent from my iPhone On Jul 16, 2007, at 2:15 PM, shacky <shacky83@gmail.com> wrote:> It depends how much IO the domUs will generate. 2xSATA isn''t that > fast... > > Couldn''t we estimate it? ~20, ~50, ~70? > _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-users_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users