Bit confused about migration, live or offline..

W

wipeout_dude

Member
Jul 15, 2012
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Can someone clarify which storage configurations do or don't support migration at all??

Then which storage configurations do or don't support live migration??

Storage options I see are..

Local directory
Local LVM
iSCSI LVM
iSCSI Direct to LUN
NFS

On the Proxmox VE storage page the only one that explicitly confirms live migration is NFS..

Thanks..
 
wipeout_dude said:
Can someone clarify which storage configurations do or don't support migration at all??

Then which storage configurations do or don't support live migration??

Storage options I see are..

Local directory
Local LVM
iSCSI LVM
iSCSI Direct to LUN
NFS

On the Proxmox VE storage page the only one that explicitly confirms live migration is NFS..

Thanks..
Click to expand...
iSCSI to LVM supports live migration. AFAIK iSCSI to direct LUN does not since you cannot migrate a direct LUN. Local does obviously not support live migration and since OpenVZ only supports local storage the live migration is not supported for OpenVZ.
 
So for clarity is this correct?

Live Migration Support
|-------------------|-KVM--|-OVZ--|
Local directory_____|___N__|__Y___|
Local LVM_________|___N__|__NA__|
iSCSI LVM_________|___Y__|__NA__|
iSCSI Direct to LUN_|___N__|__NA__|
NFS______________|___Y__|__NA__|

Is this the same for offline migration??
 
wipeout_dude said:
So for clarity is this correct?

Live Migration Support
|-------------------|-KVM--|-OVZ--|
Local directory_____|___N__|__Y___|
Local LVM_________|___N__|__NA__|
iSCSI LVM_________|___Y__|__NA__|
iSCSI Direct to LUN_|___N__|__NA__|
NFS______________|___Y__|__NA__|

Is this the same for offline migration??
Click to expand...
NFS Y Y

With offline I think everything is possible.
 
wipeout_dude said:
Storage options I see are..

Local directory
Local LVM
iSCSI LVM
iSCSI Direct to LUN
NFS

On the Proxmox VE storage page the only one that explicitly confirms live migration is NFS..

Thanks..
Click to expand...

AoE. I'm not sure about the live migration, but you can use LVM with AoE so i think it should be possible.
 
Just for the record, KVM itself supports live block migration and it works well. Sure it takes a while to migrate a large disk but IMO it's better than nothing. Then there is also incremental block migration which uses same base image on both nodes and block migrates only the COW image.

Hopefully these are integrated into Proxmox at some point.
 
this is not a stable KVM feature - or am I wrong - point me to the docs.
 
tom said:
this is not a stable KVM feature - or am I wrong - point me to the docs.
Click to expand...

I guess it is regarded as stable. Works for me (TM). I'm talking about simple "migrate -b" monitor command.

From "help" monitor command
migrate [-d] [-b] [-i] uri -- migrate to URI (using -d to not wait for completion)
-b for migration without shared storage with full copy of disk
-i for migration without shared storage with incremental copy of disk (base image shared between src and destination)



Maybe you confuse it with live block copy which is newer feature
http://www.linux-kvm.org/wiki/images/c/cf/2011-forum-qemu_live_block_copy_submit.pdf
This also works in my testings and opens up new possibilities.
 
FinnTux said:
Right. Actually I'm using 1.1 and it is still there and never had any problems. But apparently there are some issues.
Click to expand...


I would like to see this.
But when KVM 1.1 was being planned they said they were going to remove this feature:
http://www.spinics.net/lists/kvm/msg72228.html
"It don't work so well, it complicates migration code, and we are building a replacement that works."

I have tested it too, it does work, I've not had a problem.
If you look you can find people who have had issues when there is heavy IO in the VM while migrating.

Not sure if the replacement that works better is done in 1.1 or not, but I think it would be best to wait until the KVM people themselves provide a solution that they are satisfied with.
 
EDIT: after posting this, I went back and checked & found that I had clicked 'shared' for the local storage, which is NOT shared. Unclicked that, now offline migration of locally-stored VMs works. No bug, just me ;-)

------------------------------------------------------------------------------

I'm using: pve-manager/2.1/f9b0f63a with 4 nodes on my test setup. All VMs are KVM.

Using local storage, offline migration has worked fine, but I've just added a shared LVM on iSCSI, and now live migration works from one node to another for the VMs that I've moved to the shared LVM, but I can no longer migrate locally-stored VMs.

Example of attempted move of locally-stored VM 104 (vm was shut down) from node prox001 to node prox003:


Jul 21 10:02:00 starting migration of VM 104 to node 'prox003' (108.56.65.17)
Jul 21 10:02:00 copying disk images
Jul 21 10:02:01 starting VM 104 on remote node 'prox003'
Jul 21 10:02:01 ERROR: online migrate failure - command '/usr/bin/ssh -c blowfish -o 'BatchMode=yes' root@108.56.65.17 qm start 104 --stateuri tcp --skiplock' failed: exit code 255
Jul 21 10:02:03 ERROR: migration finished with problems (duration 00:00:03)
TASK ERROR: migration problems


This moved the 104.conf file to the target node but left the disk image on the original node. Fixed by manually moving 104.conf back to prox001 where the disk image was.

Am I doing something wrong or is this a bug?
 
Last edited:
"online migrate failure"

Are you sure it was properly shut down? The above could indicate that either the VM was not shut down properly or Proxmox for some reason thinks it is still running.
 
It was shut down - turns out the mistake was clicking 'shared' for the local storage (I don't remember doing that - must have been one of those 3 AM things ...).
 
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