Emiliano Gabrielli (aka AlberT)
2006-Apr-21 13:39 UTC
[Xen-users] LVM snapshot and xen stability
Hi all, anybody has any info about stability of xen (3.0.2) configurations using LVM2 r/w snapshots as domUs'' physical disks? My intention is to test the possibility of having a template VM with a base distro only and a number of snap-domUs with the differences for mail server, web server and so on.. Any experiences, tip and so on ?? Tnx in advance -- <?php echo '' Emiliano Gabrielli (aka AlberT) '',"\n", '' socio fondatore e membro del direttivo del GrUSP '',"\n", '' AlberT_at_SuperAlberT_it - www.SuperAlberT.it '',"\n", '' IRC: #php,#AES azzurra.com '',"\n",''ICQ: 158591185''; ?> _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Fri, Apr 21, 2006 at 03:39:14PM +0200, Emiliano Gabrielli (aka AlberT) wrote:> Hi all, > anybody has any info about stability of xen (3.0.2) configurations using > LVM2 r/w snapshots as domUs'' physical disks? > > My intention is to test the possibility of having a template VM with a base > distro only and a number of snap-domUs with the differences for mail server, > web server and so on.. > > Any experiences, tip and so on ?? > > Tnx in advanceCommon understanding is that LVM2 snapshots are unstable - many people see crashes and problems with snapshots. I don''t know if these problems are already fixed in Linux LVM.. Maybe someone could post real world experiences. -- Pasi _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Hi, Pasi Kärkkäinen wrote:> Common understanding is that LVM2 snapshots are unstable - many people see > crashes and problems with snapshots.I''m using LVM2 snapshots as domU filesystems on both Xen 2 and Xen 3. I haven''t really had any problems, however my usage patterns cannot be described as heavy. I''ve only had one problem and that was when a snapshot filled its allocated capacity and refused to mount. I did recover from that by editing the LVM2 header directly on the disk and backing up the data after a succesfull mount. Now I''m running a script that automatically runs "lvextend" on nearly-filled snapshot volumes. -- Taneli Leppä | Crasman Co Ltd <taneli@crasman.fi> | <http://www.crasman.fi/> _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Friday 21 April 2006 15:43, Pasi Kärkkäinen wrote:> On Fri, Apr 21, 2006 at 03:39:14PM +0200, Emiliano Gabrielli (aka AlberT)wrote:> > Hi all, > > anybody has any info about stability of xen (3.0.2) configurations > > using LVM2 r/w snapshots as domUs'' physical disks? > > > > My intention is to test the possibility of having a template VM with a > > base distro only and a number of snap-domUs with the differences for mail > > server, web server and so on.. > > > > Any experiences, tip and so on ?? > > > > Tnx in advance > > Common understanding is that LVM2 snapshots are unstable - many people see > crashes and problems with snapshots. > > I don''t know if these problems are already fixed in Linux LVM.. > > Maybe someone could post real world experiences. >My last try was very disappointing. And even if they were perfectly stable, you''d have to face another problem: You can''t just update the "base" lv and have the changes appear in all snapshots (its block based). So installing updates, security fixes etc always have to be done in each domU seperately, in the long run you won''t save much disk-space and administration trouble with it. Maybe have a look at unionfs, I''m running several domU''s mounting their (shared) root-fs read-only over NFS, and then build an writable union with a seperate vbd in their initrds. /Ernst _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Emiliano Gabrielli (aka AlberT)
2006-Apr-21 13:59 UTC
Re: [Xen-users] LVM snapshot and xen stability
On Friday 21 April 2006 15:53, Taneli Leppä wrote:> I''m using LVM2 snapshots as domU filesystems on both Xen 2 and Xen 3. > I haven''t really had any problems, however my usage patterns cannot be > described as heavy. > > I''ve only had one problem and that was when a snapshot filled > its allocated capacity and refused to mount. I did recover from > that by editing the LVM2 header directly on the disk and > backing up the data after a succesfull mount. Now I''m running > a script that automatically runs "lvextend" on nearly-filled > snapshot volumes.Yes I know this issue... what about resizing the fs over LVM? does ext3 online resize works or I''d use reiserfs if I''ll want this feature? -- <?php echo '' Emiliano Gabrielli (aka AlberT) '',"\n", '' socio fondatore e membro del direttivo del GrUSP '',"\n", '' AlberT_at_SuperAlberT_it - www.SuperAlberT.it '',"\n", '' IRC: #php,#AES azzurra.com '',"\n",''ICQ: 158591185''; ?> _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Ernst Bachmann wrote:> >Maybe have a look at unionfs, I''m running several domU''s mounting their >(shared) root-fs read-only over NFS, and then build an writable union with a >seperate vbd in their initrds. > >I do a similar thing, but without unionfs. I use tmpfs for all the directories that have to be read-write (eg. /dev, /etc), copy their content from the read-only file system to tmpfs upon the domU startup, and then mount them with "mount --bind" on top the read-only NFS root image. No issues so far...>/Ernst > >_______________________________________________ >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
I had this working fine with 3.0.1 and 2.6.12, but then ran into problems when moved (incl complete rebuild of DomU) to 2.6.16 and r1. Often, the first snapshot would run fine. Creation of further snapshot''d systems would cause the VG to lock up requiring reboot, and recreation of the entire VG. After wasting too long on it, I have moved to normal LVs, and copy the template with # cat /dev/vg/template > /dev/vg/domUn && fscj /dev/ vg/domUn And like Ernst said, changes to the template are not propagated to already established snapshots. In fact it may be precisely those changes that add to the instability. I am (using Gentoo) sharing via NFS, the /usr/portage directory, which gives me about a 1G root filesystem (no GUI), so again, Ernst is correct, it''s not a significant saving to be using snapshots. piersdd@imap-mail.com http://web.mac.com/piersdd/iWeb/Five9s/ethereality/ethereality.html On 21/04/2006, at 11:39 PM, Emiliano Gabrielli (aka AlberT) wrote:> Hi all, > anybody has any info about stability of xen (3.0.2) > configurations using > LVM2 r/w snapshots as domUs'' physical disks? > > My intention is to test the possibility of having a template VM > with a base > distro only and a number of snap-domUs with the differences for > mail server, > web server and so on.. > > Any experiences, tip and so on ?? > > Tnx in advance > -- > <?php echo '' Emiliano Gabrielli (aka AlberT) '',"\n", > '' socio fondatore e membro del direttivo del GrUSP '',"\n", > '' AlberT_at_SuperAlberT_it - www.SuperAlberT.it '',"\n", > '' IRC: #php,#AES azzurra.com '',"\n",''ICQ: 158591185''; ?> > > _______________________________________________ > 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