On Tue, 2007-11-20 at 14:06 +0100, Tomasz Chmielewski wrote: > S. J. van Harmelen schrieb: > > Thanks for your reaction! > > > > On Tue, 2007-11-20 at 12:37 +0100, Tomasz Chmielewski wrote: > >> S. J. van Harmelen schrieb: > >>> Hi list, > >>> > >>> In advance my excusses for this radar long post (although it's easy > >>> readable ;), but I want to make sure that I understand it correctly so I > >>> don't end up making a very costly mistake. > >>> > >>> I have a storage server (Debian Etch) with mutlipath-tools running and > >>> on top of that I use IET iscsi-target software to export the multipathed > >>> device to a XenSource server. > >>> > >>> XenSource creates a PV on the entire exported disk, and then creates a > >>> few LV's when I create some virtual machines. > >> Which IMO is a pity, as logically, LVM exists and is usable on that > >> given Xen server only. This means you can't really use multiple Xen > >> servers, live migration etc. > > > > Are you sure about that? Accoring to Xen lvm over iSCSI is considered as > > shared storage that can be used for live migration > > (http://docs.xensource.com/XenServer/4.0.1/installation/ch03s03.html): > > > > <snip> > > 3.3.3. XenServer Hosts with shared iSCSI storage > > This implies turning a Xen server into a NAS server, as I understand? > Yes, this should work - I have a custom Xen setup, and I don't connect a > NAS and a Xen server on one host. > But according to the description, yes, it should work. > > > (...) > > >>> Questions that I think of then are if it's not a problem that XenSource > >>> then creates a new PV and some LV's in je LV I created adn exported on > >>> the storage server. Is that a problem, or should this work fine? > >> Hmm? I don't think I understand what you mean. > > > > I mean I will have 2 sets of PV's and LV's. One set on the storage > > server (that has one PV and one LV that both span the whole disk), and > > one set op the Xen server (the ones that Xen makes by itself when I add > > a new vitrual machine). > > > > Now the one LV from the storage server that Xen sees is being exported > > true iSCSI, so it wouldn't know that it is infact a LV that it's talking > > to. As far as the Xen server conserns this is just a raw disk. So it > > will then just create the needed PV and LV's on it to provision virtual > > mahines. > > > > The question was if this PV/LV in another PV/LV (on another physical > > machine) can do any harm? > > Should work, as long as you don't use it on two different machines > (i.e., target/initiator) as LVM at the same time. > > > >>> And another question is how I can then restore a single LV Xen created, > >>> from the snapshot of the LV that spans the whole disk on the storage > >>> server? In that case I can not just revert to the old disk before taking > >>> the snapshot, because then all the LV's created by Xen will be set back > >>> to that point, and not just the LV that went bad. > >> # Will only work if snapshot size is equal or greater than > >> # the original volume > >> > >> dd if=/dev/LVM/volume-snapshot of=/dev/LVM/volume > >> > >> # or, if the allowed snapshot size is smaller, we don't want our > >> # precious snapshot dropped > >> > >> dd if=/dev/LVM/volume-snapshot of=/dev/LVM/new-volume > >> dd if=/dev/LVM/new-volume of=/dev/LVM/volume > > > > Oke, but how about this when using LVM as I just described a few lines > > above here with the PV/LV in another PV/LV setup. How can I then restore > > a snapshot of a virtual machines' LV from the snapshot of the LV on the > > storage server? > > As a prerequisite, you need to "see" that LVM. > But could you be more specific on what you want (write a bit more > details in points, write a small diagram etc.)? Oke... Let's say I have a storage server with one LUN connected to it. The LUN becomes /dev/sdi on the storage server. I will then create a PV on /dev/sdi spanning the whole disk. In the PV I will create one LV also spanning the whole disk. Say we name this LV lv_storage. So the path to this LV gets to be /dev/lvm/lv_storage. In iSCSI I will then create a target which points to /dev/lvm/lv_storage. The Xen server will use open-iscsi to connect to that target (/dev/lvm/lvstorage) and on the Xen server it becomes /dev/sdb. At this point Xen has also created a PV that spans the whole disk (/dev/sdb) Then when I create a virtual machine on the Xen server, it creates a LV on /dev/sdb with the size of the virtual disk. Say this LV gets named lv_virtualmachine1 and the next gets to be named lv_virtualmachine2 and so on. So far everything clear? Now my thoughts where to take snapshots on the storage server. So that would mean I would take a snapshot of lv_storage. This should not be a problem. But what if virtual machine 2 crashes and has to be restored? In that case I cannot restore lv_storage with a dd command, because then all the data will be restored (lv_virtualmachine1 and lv_virtualmachine2, because they are both on lv_storage). So is it possible to "restore" only lv_virtualmachine2 when I took a snapshot of lv_storage? I can see the PV and LV's Xen created on lv_storage on the storage server when I run pvs by the way... Hope you understand what I mean now? > > _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
