Hello, My supervisor wants to create a LV then give that to a VM and then create a VG with LV''s under it inside the VM. I have read on the list where this will give bad performance inside the VM. Can somebody point me to a recent, we are using 3.2, breakdown of file system performance inside of VM''s? Thanks for any advice, Jon _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> My supervisor wants to create a LV then give that to a VM and then > create a VG with LV''s under it inside the VM. I have read on the list > where this will give bad performance inside the VM.It won''t necessarily give *bad* performance but doing the two layers of translation is a bit unfortunate. What I think is perhaps more significant is the management side of things: if you''ve got two layers of LVM nested like that, it''s no longer a simple matter of just mounting a DOS partition inside an LVM volume if you want to inspect the guest''s filesystems. So it makes it harder to access an inactive guest''s filesystem (you shouldn''t mount an active guest''s filesystem, in any case). I don''t know how awkward LVM makes doing this sort of thing. To me, the simplicity of doing all LVM management in dom0 and hiding it from the guest appeals. You can easily pass through the LVs in dom0 to the guest as separate drives; if it''s a PV guest then you can even hotplug them. It''s actually possible to pass separate LVM volumes to appear as individual partitions in the guest - this has the advantage that there''s no MS-DOS partition table to worry about, just a load of linear LVs with filesystems on.> Can somebody point > me to a recent, we are using 3.2, breakdown of file system performance > inside of VM''s?Afraid I don''t have such a document. Raw disks / partitions theoretically have the highest performance as a means of storing domU disks. LVM is probably next. File-based disks are probably the lowest performers - of the two alternative implementations, tap:aio disks are supposed to be preferable to file: disks. Hope that helps some! Cheers, Mark -- Push Me Pull You - Distributed SCM tool (http://www.cl.cam.ac.uk/~maw48/pmpu/) _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Mark Williamson wrote:>> My supervisor wants to create a LV then give that to a VM and then >> create a VG with LV''s under it inside the VM. I have read on the list >> where this will give bad performance inside the VM. >> > > It won''t necessarily give *bad* performance but doing the two layers of > translation is a bit unfortunate. > >An email from Sadique on this list sometime early this year said LVM has 2% performance hit over pysical partitions. So using LVM on both dom0 and domU (roughly) reduce performance by 4%.> To me, the simplicity of doing all LVM management in dom0 and hiding it from > the guest appeals.> It''s > actually possible to pass separate LVM volumes to appear as individual > partitions in the guest - this has the advantage that there''s no MS-DOS > partition table to worry about, just a load of linear LVs with filesystems > on. > >I second that. That is what we do for Linux PV guests. Regards, Fajar _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Mon, 17 Mar 2008, Fajar A. Nugraha wrote:> Mark Williamson wrote: >>> My supervisor wants to create a LV then give that to a VM and then >>> create a VG with LV''s under it inside the VM. I have read on the list >>> where this will give bad performance inside the VM. >>> >> >> It won''t necessarily give *bad* performance but doing the two layers of >> translation is a bit unfortunate. >> >> > > An email from Sadique on this list sometime early this year said LVM has 2% > performance hit over pysical partitions. So using LVM on both dom0 and domU > (roughly) reduce performance by 4%. > >> To me, the simplicity of doing all LVM management in dom0 and hiding it >> from the guest appeals. > >> It''s actually possible to pass separate LVM volumes to appear as individual >> partitions in the guest - this has the advantage that there''s no MS-DOS >> partition table to worry about, just a load of linear LVs with filesystems >> on. >> >> > > I second that. That is what we do for Linux PV guests.For interest, how do you do this? I can see how you can make dom0 lvs appear to the pv guest as separate disks, and mke2fs each as a whole-disk file-system (without a partition table.) But is there some trick to make separate dom0 lvs appear to the domu guest as partitions on a single disk? If so, where is the partition table, and where does grub install to? Or, assuming separate disks, where does /boot go? Do you make a small (100M) lv for /boot? and how do you tell grub to boot from it - I tried it, and grub does not seem able to install itself correctly - I get: [root@domu ~ 0]$ grub-install /dev/hda Unknown partition table signature Unknown partition table signature Unknown partition table signature Unknown partition table signature Unknown partition table signature The file /boot/grub/stage1 not read correctly. [root@domu ~ 1]$ Am I missing something obvious? (using Centos 5.1 x86_64 as dom0 and domu)> > Regards, > > Fajar > >_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users