Subject: Re: [vserver] tcpdump, top, mpstat, iostat
From: Herbert Poetzl <herbert@13thfloor.at>
Date: Fri, 7 Jan 2011 02:08:16 +0100

On Fri, Jan 07, 2011 at 10:01:46AM +0900, Andrej van der Zee wrote:
> Dear Herbert,

> Thank you for your prompt reply.

> > > iostat.
> > no device stats available inside a guest

> I am not much of a kernel expert and this might be 
> an obvious question, but I am interested in why these 
> are not available in the guest, and is there any 
> chance they will be in the future?

mainly because device I/O is shared between all the
guests (usually residing on the same filesystem) and
there is no simple way to tell which guest caused
what I/O ... there is some work done to limit and
classify I/O access for cgroups, but it's more to
limit a certain group in total I/O than do the rather
precise accounting per device.

note that I do not see a good reason to do that
accounting for or from within a guest, if you want
to monitor I/O to devices, IMHO the host is the best
place to do so (same for network statistics)

so, unless somebody finds this feature so increadibly
usefull that s/he decides to sponsor development in
this direction, I doubt it will ever get implemented.

best,
Herbert

> Thank you,
> Andrej