Hi, Is there any way you can save a xen domain without suspending it or stopping it? I want to set up something so if my xen session crashes I can fire up another xen session from the save file that I created 5 minutes before the crash and hopefully minimize downtime. Thanks -- ------------------------------ Christopher Vaughan
On Thu, Jun 29, 2006 at 04:56:21PM -0600, Chris Vaughan wrote:> Hi, > > Is there any way you can save a xen domain without suspending it or stopping > it? I want to set up something so if my xen session crashes I can fire up > another xen session from the save file that I created 5 minutes before the > crash and hopefully minimize downtime.Doesn''t work in general because you would have to save the state of the filesystems too. Xen operations don''t allow a save and continue for that reason I was told. Daniel -- Daniel Veillard | Red Hat http://redhat.com/ veillard@redhat.com | libxml GNOME XML XSLT toolkit http://xmlsoft.org/ http://veillard.com/ | Rpmfind RPM search engine http://rpmfind.net/
So what''s the difference between a "Live Migration" & "Save" then? Does the live migration keep the image open and the save does not? To me they seam to be 2 peas in a pod but I guess I''m mistaken. Thanks On 6/29/06, Daniel Veillard <veillard@redhat.com> wrote:> > On Thu, Jun 29, 2006 at 04:56:21PM -0600, Chris Vaughan wrote: > > Hi, > > > > Is there any way you can save a xen domain without suspending it or > stopping > > it? I want to set up something so if my xen session crashes I can fire > up > > another xen session from the save file that I created 5 minutes before > the > > crash and hopefully minimize downtime. > > Doesn''t work in general because you would have to save the state of the > filesystems too. Xen operations don''t allow a save and continue for that > reason I was told. > > Daniel > > -- > Daniel Veillard | Red Hat http://redhat.com/ > veillard@redhat.com | libxml GNOME XML XSLT toolkit http://xmlsoft.org/ > http://veillard.com/ | Rpmfind RPM search engine http://rpmfind.net/ >-- ------------------------------ Christopher Vaughan
Chris Vaughan wrote:> So what''s the difference between a "Live Migration" & "Save" then? Does > the live migration keep the image open and the save does not? To me > they seam to be 2 peas in a pod but I guess I''m mistaken. > > Thanks > >Migration saves VM state and assumes that the filesystem does not change. Checkpointing would have to restore the filesystem to the same point in time that the snapshot was taken of the VM. Perhaps you could swing it with CoW or something, but it doesn''t work now. -- Christopher G. Stach II
On Thu, Jun 29, 2006 at 05:14:11PM -0600, Chris Vaughan wrote:> So what''s the difference between a "Live Migration" & "Save" then? Does the > live migration keep the image open and the save does not? To me they seam > to be 2 peas in a pod but I guess I''m mistaken.Live migration ensures that the filesystem is passed as is from one state to the other. Restoring a checkpointed system would mean that the system would suddenly warp back in time wrt to the filesystem, or what is effectively the same from the system''s POV the filesystem suddenly warped ahead in time. For example: Perhaps your crash between the checkpointing and the resuming was caused by rm -fr / and no checkpointing could undo that :) So checkpointing in xen would only work hand in hand with block device snapshoting.> Thanks > > > On 6/29/06, Daniel Veillard <veillard@redhat.com> wrote: > > > >On Thu, Jun 29, 2006 at 04:56:21PM -0600, Chris Vaughan wrote: > >> Hi, > >> > >> Is there any way you can save a xen domain without suspending it or > >stopping > >> it? I want to set up something so if my xen session crashes I can fire > >up > >> another xen session from the save file that I created 5 minutes before > >the > >> crash and hopefully minimize downtime. > > > > Doesn''t work in general because you would have to save the state of the > >filesystems too. Xen operations don''t allow a save and continue for that > >reason I was told. > > > >Daniel > > > > >-- Axel.Thimm at ATrpms.net
Christopher G. Stach II wrote:> Migration saves VM state and assumes that the filesystem does not > change. Checkpointing would have to restore the filesystem to the same > point in time that the snapshot was taken of the VM. Perhaps you could > swing it with CoW or something, but it doesn''t work now.So take an LVM snapshot of the filesystem also. Maintaining network state would seem to be the harder thing to me. -- Tracy R Reed http://ultraviolet.org
Tracy R Reed wrote:> Christopher G. Stach II wrote: >> Migration saves VM state and assumes that the filesystem does not >> change. Checkpointing would have to restore the filesystem to the same >> point in time that the snapshot was taken of the VM. Perhaps you could >> swing it with CoW or something, but it doesn''t work now. > > So take an LVM snapshot of the filesystem also. Maintaining network > state would seem to be the harder thing to me. >There was talk of weaving Cruz into Xen: http://www.hpl.hp.com/techreports/2005/HPL-2005-66.pdf -- Christopher G. Stach II
tbrown@baremetal.com wrote:> network state is part of the kernel memory that is saved and/or > migrated.... so that doesn''t seem to be an issue.Right but that is only network state as of when the kernel memory was saved. The tcp stream (for example) has moved on since then. If I am scp''ing a file and suddenly the server reverts to the state of 5 seconds ago, the connection will die for sure. If the incorrect TCP sequence numbers didn''t kill it the cipher block chaining of ssh certainly would. You basically have to constantly stream the current network state to some storage medium in real time. Around 6 years ago I had a pair of Network Appliance machines...F750 I think they were. They would actually do this. They came with some big fat cable you would connect them with and they would maintain the state of every network transaction in real time over that interconnect so that if one machine died the other could take over without dropping the connections. It was pretty sweet. Perhaps some day xen will be able to achieve this sort of high availability using a similar technique. -- Tracy R Reed http://ultraviolet.org _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users