Back when I started messing with Xen (a year or so ago), I read where it was not good to have a domu setup with LVM inside of it if the storage on the Dom0 was LVM also. Basically this would be a nested LVM situation or similar. However, I find myself installing more and more CentOS domu''s since my Dom0 machine has to be CentOS to use the dell OMSA stuff for monitoring and all. This is not an issue, other than by default CentOS uses LVM and I have to manually edit the partition table of the domu. Is there any benefit/drawback to having/not having LVM domu''s? Here are a few I can think of off the top of my head: Good reason to have LVM in domu: internal snapshot feature "plug and play" with a centos system (no manually editing the partition table on install) Possible drawbacks to having LVM in domu: cannot mount /dev/foo/lv from dom0 and see filesystem possible slowdown? Looking for any and all feedback on this. Thanks in advance! -- Donny B. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Tue, Apr 13, 2010 at 4:34 AM, Donny Brooks <dbrooks@mdah.state.ms.us> wrote:> Back when I started messing with Xen (a year or so ago), I read where it was not good to have a domu setup with LVM inside of it if the storage on the Dom0 was LVM also."not good" is relative. RedHat would say its benefit outweights its drawbacks.> Basically this would be a nested LVM situation or similar. However, I find myself installing more and more CentOS domu''s since my Dom0 machine has to be CentOS to use the dell OMSA stuff for monitoring and all. This is not an issue, other than by default CentOS uses LVM and I have to manually edit the partition table of the domu. > > > Is there any benefit/drawback to having/not having LVM domu''s? Here are a few I can think of off the top of my head: > > Good reason to have LVM in domu: > internal snapshot feature > "plug and play" with a centos system (no manually editing the partition table on install)You could always put non-LVM partition layout (as well as package selection and other stuffs) on a kickstart file, so no "manually editing the partition table" would be necessary.> > Possible drawbacks to having LVM in domu: > cannot mount /dev/foo/lv from dom0you could, if the VG on dom0 have different name from domU.> and see filesystem > possible slowdown?If you have RHN subscription you might be able to ask them what the performance penalty given by LVM is. AFAIK is negligible. -- Fajar _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Mon, Apr 12, 2010 at 8:11 PM, Fajar A. Nugraha <fajar@fajar.net> wrote:> On Tue, Apr 13, 2010 at 4:34 AM, Donny Brooks <dbrooks@mdah.state.ms.us> > wrote: > > Back when I started messing with Xen (a year or so ago), I read where it > was not good to have a domu setup with LVM inside of it if the storage on > the Dom0 was LVM also. > you could, if the VG on dom0 have different name from domU. > > > and see filesystem > > possible slowdown? > > If you have RHN subscription you might be able to ask them what the > performance penalty given by LVM is. AFAIK is negligible. > > -- > Fajar > >I''ve done a lot of testing on LVM performance and it''s almost alway as fast or within 10% of the speed of non-LVM at the worst. I too think the benefits outweight the negatives. Grant McWilliams _______________________________________________ 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 Fajar A. Nugraha > > On Tue, Apr 13, 2010 at 4:34 AM, Donny Brooks<dbrooks@mdah.state.ms.us>> wrote: > > Back when I started messing with Xen (a year or so ago), I readwhere it was not> good to have a domu setup with LVM inside of it if the storage on theDom0 was LVM> also. > > "not good" is relative. RedHat would say its benefit outweights itsdrawbacks. The "benefit" I can see is that the domU disk image with partitions and LVM remains compatible with Kickstart. But there are other ways to bootstrap a Red Hat or CentOS image. I''m seeing us move rapidly towards a model in which all our hosts are virtualized, but the Linux distribution we use remains encumbered by features designed for bare iron deployments. I hope a new OS will emerge some day--one optimized for virtualization. Eliminate the old-fashioned boot loader, disk partitions, block schedulers, RAID options, etc. Move simple network services into dom0, or maybe stubdom. Basic Red Hat installs now require 1GB+ disk and 256MB RAM to be usable. That''s because the OS bundles every package it will need to run standalone on bare iron. I realize disk/memory are now a cheap commodity but the bloat reminds me of some of the reasons I left behind a certain proprietary OS. -Jeff _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Tuesday, April 13, 2010 09:35 AM CDT, Jeff Sturm <jeff.sturm@eprize.com> wrote:> > -----Original Message----- > > From: xen-users-bounces@lists.xensource.com [mailto:xen-users- > > bounces@lists.xensource.com] On Behalf Of Fajar A. Nugraha > > > > On Tue, Apr 13, 2010 at 4:34 AM, Donny Brooks > <dbrooks@mdah.state.ms.us> > > wrote: > > > Back when I started messing with Xen (a year or so ago), I read > where it was not > > good to have a domu setup with LVM inside of it if the storage on the > Dom0 was LVM > > also. > > > > "not good" is relative. RedHat would say its benefit outweights its > drawbacks. > > The "benefit" I can see is that the domU disk image with partitions and > LVM remains compatible with Kickstart. But there are other ways to > bootstrap a Red Hat or CentOS image. > > I''m seeing us move rapidly towards a model in which all our hosts are > virtualized, but the Linux distribution we use remains encumbered by > features designed for bare iron deployments. I hope a new OS will > emerge some day--one optimized for virtualization. Eliminate the > old-fashioned boot loader, disk partitions, block schedulers, RAID > options, etc. Move simple network services into dom0, or maybe stubdom. > > Basic Red Hat installs now require 1GB+ disk and 256MB RAM to be usable. > That''s because the OS bundles every package it will need to run > standalone on bare iron. I realize disk/memory are now a cheap > commodity but the bloat reminds me of some of the reasons I left behind > a certain proprietary OS. > > -Jeff > > > > _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-usersJeff, The bloat is exactly why I personally prefer ubuntu over CentOS. They have the JeOS where you can install a functional machine in under 300MB disk and 128MB ram. But trying to get the OMSA stuff installed for a Dell server on anything but a rpm based distro is near futile. So alas, I am having to deal with CentOS. One good thing about Xen is you can have ready made images. This is one thing I have found myself using more and more recently. -- Donny B. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Tue, Apr 13, 2010 at 7:56 AM, Donny Brooks <dbrooks@mdah.state.ms.us>wrote:> > > > Jeff, > > The bloat is exactly why I personally prefer ubuntu over CentOS. They > have the JeOS where you can install a functional machine in under 300MB disk > and 128MB ram. But trying to get the OMSA stuff installed for a Dell server > on anything but a rpm based distro is near futile. So alas, I am having to > deal with CentOS. One good thing about Xen is you can have ready made > images. This is one thing I have found myself using more and more recently. > > -- > > Donny B. > > >I generally forget how to install CentOS on Xen each time I do it since I rarely install anymore. The beauty of Virtualization is you''re always using the same "hardware" so you can customize one installation and just use that as a base. In that case I can justify figuring out what I don''t need and uninstalling it. Grant McWilliams _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Donny Brooks <dbrooks@mdah.state.ms.us> writes:> Possible drawbacks to having LVM in domu: > cannot mount /dev/foo/lv from dom0 and see filesystemYou can, but be careful: you can activate the domU''s VG in the dom0 even while the domU is still running, but you mustn''t do any LVM operations during this period (unless you use clvm, which is probably overkill). Contrast this with mounting the domU''s file system on the dom0 while it''s still mounted on the domU: this is ALWAYS a disaster (unless you use some cluster file system, which is probably overkill). Based on this, I always use a strict filter in my lvm.conf in the dom0, so that it can''t accidentally activate the domUs'' VGs. If I want to mount some domU filesystem on the dom0, I extend the filter to include the given dom0 LV (which is a PV from the domU''s point of view), activate the domU''s VG (all my VGs have different names, and yours should, too: just use the hostnames), do my business, deactivate the domU''s VG and close down the filter again. This works and is rather safe.> possible slowdown?That shouldn''t be measurable. -- Cheers, Feri. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> > Possible drawbacks to having LVM in domu: > cannot mount /dev/foo/lv from dom0 and see filesystem > possible slowdown? > > Looking for any and all feedback on this. Thanks in advance! >My (very short, I advise) experience on that topic was bad enough to make me give up on using LVM over LVM. Yes, I agree that would the ideal scenario for storage managment, but after running some basic I/O tests (with IOZone[1]) I found out that performance went to the ground drastically. Ok, maybe I''m being a litte dramatic here, but I really had a significant decrease on I/O write and read rates after adding a second LVM layer on domU. So, I abandoned this idea and kept LVM only on dom0 side. That''s my particular point of view, but not take it as a rule. You should perform your own tests and see what you get. [1] http://www.iozone.org/ _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users