Re: [Xen-users] Why is xen allocating entire disk/file?

[Charlie Reddington <charlie.reddington@xxxxxxxxx>]

On Jan 28, 2009, at 11:30 PM, Fajar A. Nugraha wrote:

> On Thu, Jan 29, 2009 at 12:20 PM, Charlie Reddington
> <charlie.reddington@xxxxxxxxx> wrote:
> > # df -h
> > Filesystem            Size  Used Avail Use% Mounted on
> > /dev/sda1             446G   43G  381G  10% /
> > tmpfs                 3.9G     0  3.9G   0% /dev/shm
> >
> > Right here alone, has me kind of sketcy. Total - 446G - 43G should  
> > = 403G
> No comment on that one :)
>
> > But in var/lib/xen/images.....
> >
> > # du -sh *
> > 9.8G    ns1.img
> > 9.8G    ns2..img
> > 119M    shared01.img
> > 20G             www.img
> >
> > Doing the command as you say.....
> >
> > 9.8G -rwxrwxr-x 1 root root 9.8G Jan 28 15:18 ns1.img
> > 9.8G -rwxrwxr-x 1 root root 9.8G Jan 28 15:18 ns2.img
> > 134M -rwxrwxr-x 1 root root  98G Jan 28 15:18 shared01.img
> > 20G -rwxrwxr-x 1 root root  20G Jan 28 15:18 www.img
> So it doesn't use 100G right away, right?
> Both "du -sh" and "ls -lash" (leftmost column) shows space actually
> used. It can be different from the right column if it's created as
> sparse file (in your case, "not to allocate the entire disk yet").
>
> > I'm just overall kind of confused how this is working.  I should in  
> > theory
> > be able to over allocate a number of vm's, so that when I get close  
> > to
> > running out, I can just add more disk space as cash allows.
> Yes, it should work like that. Note however that using sparse file has
> the downside of :
> - lower I/O performance initially (i.e. only when it has to allocate
> disk space previously used)
> - there might be a condition when you run out of space (e.g. when all
> domU unexpectedly needs more space) which can lead to unpredictable
> result.
>
> Regards,
>
> Fajar
Thanks for the reply. I'm just trying to get the most out of this  
stuff as we are not. We'll be adding a lot more storage in the future,  
but are working on getting things going. I just want everything to  
have the ability to expand as it needs, and we should have everything  
in place before running out of disk space is an issue.
So, since it's calling the file 100gb, but only use 20, will I run  
into any problems on the host system thinking it's out of memory?  
That's really probably my only concern. If I setup 10vms and I'm over  
by a 100gb or so, will the host os complain?
Thanks,

Charlie

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