For a stable deployable, yet flexible solution, what VBD types do people here reommend. I know from the Documentation (and common-sense) that file-backed vbd''s will die for I/O intensive activities, so I''m leaning towards LVM as a solution. One thing that has caught my eye is the snapshot ability for a logical volume, but after a little more research and dipping into the archives I''ve heard nightmare stories with using snapshots with Xen. Is this still the case. Am I just better off simply installing domains as I need them? Thanks. -- Regards, Alex Adranghi --------------------------- http://www.alexadranghi.com mail@alexadranghi.com _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> > I''m currently using snapshotting for backup purposes, snapshotting > around 20 LVs every 20 minutes and mounting them in dom0. > > I haven''t had any problems with this except that with 256M RAM my > dom0 ran out of kernel memory and an lvcreate operation deadlocked. > I reported this to the LVM list and was told it was because I had > too little RAM. After upgrading dom0 to 512M I have had no such > problems, although I still am not sure exactly how much RAM each > snapshot will need. > > Today I saw a question on the linux-lvm list asking if snapshots > were considered stable in LVM2 now. Maybe following that thread > would be more helpful than my anecdotes.Thanks. Although this is relevent to what I''m wanting to do, what I meant to say was using lvm snapshots as a way to reduce common files from repeating on disk. I quote the LVM-HowTo as it explains it a little better. "It is also useful for creating volumes for use with Xen. You can create a disk image, then snapshot it and modify the snapshot for a particular domU instance. You can then create another snapshot of the original volume, and modify that one for a different domU instance. Since the only storage used by a snapshot is blocks that were changed on the origin or the snapshot, the majority of the volume is shared by the domU''s."> > How do you mean? If you start domains that you don''t need then the > RAM is tied up in those domains. If you wanted some other domain to > increase its RAM then it may be a laborious process taking a bit of > RAM from multiple other domains first. Also the idle processes in > all those domains would take a small amount of CPU away. Those are > about the only problems I can see with running domains you don''t > immediately need.I mean''t as in create them when they are needed, rather than start them sorry. Thanks -- Regards, Alex Adranghi --------------------------- http://www.alexadranghi.com mail@alexadranghi.com _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Mon, Jun 20, 2005 at 05:23:26PM +0100, Alex Adranghi wrote:> For a stable deployable, yet flexible solution, what VBD types do people > here reommend. > > I know from the Documentation (and common-sense) that file-backed vbd''s > will die for I/O intensive activities, so I''m leaning towards LVM as a > solution.I use LVM for that reason and just because I''m familiar with LVM alreayd and see no need to be adding file-backed VBDs into the mix.> One thing that has caught my eye is the snapshot ability for a logical > volume, but after a little more research and dipping into the archives > I''ve heard nightmare stories with using snapshots with Xen. Is this > still the case.I''m currently using snapshotting for backup purposes, snapshotting around 20 LVs every 20 minutes and mounting them in dom0. I haven''t had any problems with this except that with 256M RAM my dom0 ran out of kernel memory and an lvcreate operation deadlocked. I reported this to the LVM list and was told it was because I had too little RAM. After upgrading dom0 to 512M I have had no such problems, although I still am not sure exactly how much RAM each snapshot will need. Today I saw a question on the linux-lvm list asking if snapshots were considered stable in LVM2 now. Maybe following that thread would be more helpful than my anecdotes.> Am I just better off simply installing domains as I need them? Thanks.How do you mean? If you start domains that you don''t need then the RAM is tied up in those domains. If you wanted some other domain to increase its RAM then it may be a laborious process taking a bit of RAM from multiple other domains first. Also the idle processes in all those domains would take a small amount of CPU away. Those are about the only problems I can see with running domains you don''t immediately need. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Am Montag, den 20.06.2005, 18:11 +0100 schrieb Alex Adranghi: [...]> Thanks. Although this is relevent to what I''m wanting to do, what I > meant to say was using lvm snapshots as a way to reduce common files > from repeating on disk. I quote the LVM-HowTo as it explains it a little > better. > > "It is also useful for creating volumes for use with Xen. You can create > a disk image, then snapshot it and modify the snapshot for a particular > domU instance. You can then create another snapshot of the original > volume, and modify that one for a different domU instance. Since the > only storage used by a snapshot is blocks that were changed on the > origin or the snapshot, the majority of the volume is shared by the > domU''s."[...] We use the device-mapper for this. Works for us [tm]: dd if=/dev/zero of=/tmp/CoW1 bs=1M count=$CoW_SIZE dd if=/dev/zero of=/tmp/CoW2 bs=1M count=$CoW_SIZE losetup /dev/loop0 root_fs losetup /dev/loop1 /tmp/CoW1 losetup /dev/loop2 /tmp/CoW2 BLOCKSIZE=`blockdev --getsize /dev/loop0` echo "0 $BLOCKSIZE linear /dev/loop0 0" \ | dmsetup create rootfs_base echo "0 $BLOCKSIZE snapshot /dev/mapper/rootfs_base /dev/loop1 p 8" \ | dmsetup create rootfs1 echo "0 $BLOCKSIZE snapshot /dev/mapper/rootfs_base /dev/loop2 p 8" \ | dmsetup create rootfs2 You should now be able to use /dev/mapper/rootfs{1|2} read/write. Only diff blocks to "root_fs" get written to "/tmp/CoW{1|2}". This way we boot >20 domUs off one root_fs (after shutdown we delete the CoW files). I have now clue how to do that with LVM[2]. /nils. -- there is no sig _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users