Hi all, While I''ve read some faqs, forums and Professional Xen Virtualization, I would like your take on this. I''ve 2 paravirtualized domUs running, each using tap:aio disk image located on a local 500GB raid. While performance seems fine both interactively and using benchmarks, is there a practical limit to the image size before I should start breaking it up? I plan to build another dom0 box with a 24TB raid on it and hosting 2 paravirtualized domUs, one of which will need 20TB. Should I break up the domU into 2 images, 1 for the OS and the other for storage needs? So my questions are; 1 - Whats a practical single disk image size? 2 - Should I pre allocate all image space during domU creation or have it dynamically grow? - Brian _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Tue, Jan 6, 2009 at 12:58 PM, Brian Krusic <brian@krusic.com> wrote:> Hi all, > > While I''ve read some faqs, forums and Professional Xen Virtualization, I > would like your take on this. >You should read Running Xen ;)> I''ve 2 paravirtualized domUs running, each using tap:aio disk image located > on a local 500GB raid. > > While performance seems fine both interactively and using benchmarks, is > there a practical limit to the image size before I should start breaking it > up? >If there is a hard limit on the file system for max file size that is could be an issue. Otherwise, it can really depend on usage, backup considerations, etc.> I plan to build another dom0 box with a 24TB raid on it and hosting 2 > paravirtualized domUs, one of which will need 20TB. > > Should I break up the domU into 2 images, 1 for the OS and the other for > storage needs? >This can be beneficial in a general sense, for backup purposes and also performance could be achieved, just like with a non-virtualized system writing to different physical disks.> So my questions are; > > 1 - Whats a practical single disk image size?Others may have experience with very large disks....> 2 - Should I pre allocate all image space during domU creation or have it > dynamically grow? >It depends on performance needed. Dynamically growing will have some performance degradation. And the dynamically allocated ones will save you a lot of space. It is a trade off. In practice, if breaking up, you could have a mixture of disks, the performance crucial ones could be pre-allocated and the less performance crucial, less used, could be dynamically grown (aka sparse files). Hope that helps some. Cheers, Todd -- Todd Deshane http://todddeshane.net http://runningxen.com _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> While performance seems fine both interactively and using benchmarks, > is there a practical limit to the image size before I should start > breaking it up?I do *everything* through physical allocations -- phy: -- and I''m quite happy with it. tap:aio seems like unnecessary overhead. John -- John Madden Sr. UNIX Systems Engineer Ivy Tech Community College of Indiana jmadden@ivytech.edu _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Tue, Jan 6, 2009 at 1:56 PM, John Madden <jmadden@ivytech.edu> wrote:>> While performance seems fine both interactively and using benchmarks, >> is there a practical limit to the image size before I should start >> breaking it up? > > I do *everything* through physical allocations -- phy: -- and I''m quite happy > with it. tap:aio seems like unnecessary overhead. > > John >LVM? Raid? Normal Partitions? There are some general rules on what is faster, but has there been any comprehensive studies on the different disks types? Thanks, Todd -- Todd Deshane http://todddeshane.net http://runningxen.com _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Tue, Jan 6, 2009 at 12:07 PM, Todd Deshane <deshantm@gmail.com> wrote:> On Tue, Jan 6, 2009 at 1:56 PM, John Madden <jmadden@ivytech.edu> wrote: > >> While performance seems fine both interactively and using benchmarks, > >> is there a practical limit to the image size before I should start > >> breaking it up? > > > > I do *everything* through physical allocations -- phy: -- and I''m quite > happy > > with it. tap:aio seems like unnecessary overhead. > > > > John > > >It''s amazing how little that overhead is though. I''ve done extensive testing on native LVM, file: and tap:aio and I think most people would be surprised at how well Xen handles disk files. Dom0 LVM is faster than a DomU in a tap:aio file but not in all benchmarks and not by much when it is. Maximum was 20% speed increase over tap:aio in the extreme case. Half the tests show that the speed difference between the two is within the error range of the test. Yes phy: is faster but I''d only use it in those cases where I absolutely had to have the last bit of disk performance. It always feels a bit hackish to have your DomUs running out of a disk file but I wouldn''t choose another method based on perfomance. Disk files do have other advantages. All of my test results will be released in my upcoming Virt-Report. I have a lot of work still to do. Grant McWilliams Some people, when confronted with a problem, think "I know, I''ll use Windows." Now they have two problems. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Tuesday 06 January 2009 03:07:20 pm Todd Deshane wrote:> > I do *everything* through physical allocations -- phy: -- and I''m quite > > happy with it. tap:aio seems like unnecessary overhead. > > > > John > > LVM? > Raid? > Normal Partitions?I deal mostly with SAN LUNs, but at least RAID and normal partitions would work, maybe not LVM due to the lvm-within-lvm thing, but I haven''t played with that and I''m sure someone else has. John -- John Madden Sr. UNIX Systems Engineer Ivy Tech Community College of Indiana jmadden@ivytech.edu _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users