Hi, I had the initial idea that it would be more space economic if I''d add a large swap space to Dom0 and do not assign individual DomUs any swap. However I had in mind that XNE would also give virtual memory to DomUs as RAM (virtually). It seems that Dom0 can only give out physical RAM as virtual RAM for DomUs. Is that correct? The other question is: Does something like a "cluster swap partition" exist (in a sense of cluster file system, where all DomUs could swap to)? And when we are at it: Did anybody manage to share a local filesystem using some cluster filesystem between DomUs? I''m thinking about being space efficient. Regards, Ulrich _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Hi Ulrich,> I had the initial idea that it would be more space economic if I''d add a > large > swap space to Dom0 and do not assign individual DomUs any swap. However I > had in > mind that XNE would also give virtual memory to DomUs as RAM (virtually). > It seems > that Dom0 can only give out physical RAM as virtual RAM for DomUs. Is that > correct?In Xen, you can only prorate things, which are physically there. You can''t overcommit anything. If you want to do so, you''ve to use Virtuozo or its free counterpart. In Xen, every DomU has to do its own swapping, so that it could not thwart other DomUs.> I''m thinking about being space efficient.The Xen answer: Hard drive space is cheap in these days. Gruß, cp -- Die Homepage meines Vertrauens: www.cpur.de _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On 17 Oct 2006 at 11:26, Christoph Purrucker wrote:> The Xen answer: Hard drive space is cheap in these days. >If an OS installation needs about 4GB for filesystem, and the application demands 20GB of swap (because of some lousy memory management), you''ll need around 24GB of disk space per DomU. As the server only has a 73GB disk (2.5" in a 1U rack server), space is limited. Nevertheless: Saving is always better than wasting. Regards, Ulrich _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> -----Original Message----- > From: xen-users-bounces@lists.xensource.com > [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of > Ulrich Windl > Sent: 17 October 2006 14:47 > To: Christoph Purrucker > Cc: xen-users@lists.xensource.com > Subject: Re: [Xen-users] Q: swap and where? > > On 17 Oct 2006 at 11:26, Christoph Purrucker wrote: > > > The Xen answer: Hard drive space is cheap in these days. > > > > If an OS installation needs about 4GB for filesystem, and the > application demands > 20GB of swap (because of some lousy memory management), > you''ll need around 24GB of > disk space per DomU. As the server only has a 73GB disk (2.5" > in a 1U rack > server), space is limited.But you''ll need 20GB of space (per guest) somewhere whichever way you do it - unless of course you have some special knowledge about the problem that explains that this will only happen predictably and sometimes so you can decide beforehand that you only need (say) a total of 40GB to hold 4 guests, because only two at a time will need 20GB... If that''s the case, perhaps Xen is a bad choice. But if you don''t know when and how much memory each guest will need, you''ll still need the space per guest, no matter what technology is used to give the virtual memory-space to the guest... -- Mats> > Nevertheless: Saving is always better than wasting. > > Regards, > Ulrich > > > _______________________________________________ > 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
On 17 Oct 2006 at 15:52, Petersson, Mats wrote: [...]> But you''ll need 20GB of space (per guest) somewhere whichever way you do > it - unless of course you have some special knowledge about the problem > that explains that this will only happen predictably and sometimes so > you can decide beforehand that you only need (say) a total of 40GB to > hold 4 guests, because only two at a time will need 20GB... If that''s > the case, perhaps Xen is a bad choice. But if you don''t know when andThe software vendor says it needs it, but in my experience it never actually needs it...> how much memory each guest will need, you''ll still need the space per > guest, no matter what technology is used to give the virtual > memory-space to the guest... > > -- > Mats[...] _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> -----Original Message----- > From: xen-users-bounces@lists.xensource.com > [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of > Ulrich Windl > Sent: 17 October 2006 15:36 > To: Petersson, Mats > Cc: xen-users@lists.xensource.com > Subject: RE: [Xen-users] Q: swap and where? > > On 17 Oct 2006 at 15:52, Petersson, Mats wrote: > > [...] > > But you''ll need 20GB of space (per guest) somewhere > whichever way you do > > it - unless of course you have some special knowledge about > the problem > > that explains that this will only happen predictably and > sometimes so > > you can decide beforehand that you only need (say) a total > of 40GB to > > hold 4 guests, because only two at a time will need 20GB... > If that''s > > the case, perhaps Xen is a bad choice. But if you don''t > know when and > > The software vendor says it needs it, but in my experience it > never actually needs > it...Ok, so you can then use a smaller swap and only enlarge it if the system crashes with "out of swap". That should work... -- Mats _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> I had the initial idea that it would be more space economic if I''d add a > large swap space to Dom0 and do not assign individual DomUs any swap. > However I had in mind that XNE would also give virtual memory to DomUs as > RAM (virtually). It seems that Dom0 can only give out physical RAM as > virtual RAM for DomUs. Is that correct?Virtual machines under Xen get a real allocation of physical memory, they''re not paged by either dom0 or Xen itself. This avoids a few potential issues (e.g. "double paging") and makes the implementation simpler. The argument that goes along with this is that the domUs themselves are best placed to understand which bits should be swapped out, so they should be in charge of swapping their own stuff. As a result of this, they all need to have swap partitions.> The other question is: Does something like a "cluster swap partition" exist > (in a sense of cluster file system, where all DomUs could swap to)?Nope. You could use VBDs backed by sparse files to hold the domU swap partitions. That would mean that space wasn''t used on the real disk until the actual domU filled it with something (although obviously, eventually you''d probably end up with every bit of the file being used, making it non-sparse and therefore nolonger a space saving).> And > when we are at it: Did anybody manage to share a local filesystem using > some cluster filesystem between DomUs?I''m pretty sure this has been done, yes. Cheers, Mark> I''m thinking about being space efficient. > > Regards, > Ulrich > > > _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-users-- Dave: Just a question. What use is a unicyle with no seat? And no pedals! Mark: To answer a question with a question: What use is a skateboard? Dave: Skateboards have wheels. Mark: My wheel has a wheel! _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Sat, Oct 21, 2006 at 04:32:22AM +0100, Mark Williamson wrote:> > Virtual machines under Xen get a real allocation of physical memory, they''re > not paged by either dom0 or Xen itself. This avoids a few potential issues > (e.g. "double paging") and makes the implementation simpler. > > The argument that goes along with this is that the domUs themselves are best > placed to understand which bits should be swapped out, so they should be in > charge of swapping their own stuff. As a result of this, they all need to > have swap partitions.OTOH it could be nice to do this. As $software-vendor says ''i support my application on servers with 20GB swap'' and you can work around this with sparse-files, its nice to have vm-memory swapped out on dom0. vmware supports this, would be nice to know how often it is used. Christian _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users