[Openstack] KVM live block migration: stability, future, docs

Huang Zhiteng winston.d at gmail.com
Wed Aug 8 01:50:20 UTC 2012


> But to the contrary. I tested live-migrate (without block migrate)
> last night using a guest with 8GB RAM (almost fully committed) and
> lost any access/contact with the guest for over 4 minutes - it was
> paused for the duration. Not something I'd want to do to a user's
> web-server on a regular basis...

4 minutes of pause (down time)?  That's way too long.  Even there was
crazy memory intensive workload inside the VM being migrated, the
worst case is KVM has to pause VM and transmit all 8 GB memory (all
memory are dirty, which is very rare).  If you have 1GbE link between
two host, that worst case pause period (down time) is less than 2
minutes.  My previous experience is: the down time for migrating one
idle (almost no memory access) 8GB VM via 1GbE is less than 1 second;
the down time for migrating a 8 GB VM that page got dirty really
quickly is <60 seconds.  FYI.

-- 
Regards
Huang Zhiteng




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