在 11/2/22 1:57 AM, David Teigland 写道:
On Wed, Nov 02, 2022 at 01:02:27AM +0800, Zhiyong Ye wrote:
Hi Dave,
Thank you for your reply!
Does this mean that there is no way to live migrate VMs when using lvmlockd?
You could by using linear LVs, ovirt does this using sanlock directly,
since lvmlockd arrived later.
Yes, standard LV is theoretically capable of live migration because it
supports multiple hosts using the same LV concurrently with a shared
lock (lvchange -asy). But I want to support the live migration feature
for both LVs (thin LV and standard LV).
As you describe, the granularity of thinlv's sharing/unsharing is per
read/write IO, except that lvmlockd reinforces this limitation for the lvm
activation command.
Is it possible to modify the code of lvmlockd to break this limitation and
let libvirt/qemu guarantee the mutual exclusivity of each read/write IO
across hosts when live migration?
lvmlockd locking does not apply to the dm i/o layers. The kind of
multi-host locking that you seem to be talking about would need to be
implemented inside dm-thin to protect on-disk data structures that it
modifies. In reality you would need to write a new dm target with locking
and data structures designed for that kind of sharing.
I can try to write a new dm thin target or make some modifications based
on the existing dm-thin target to support this feature, if it is
technically feasible. But I'm curious why the current dm-thin doesn't
support multi-host shared access, just like dm-linear does.
Regards!
Zhiyong
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