[openstack-dev] [cinder] LVM snapshot performance issue -- why isn't thin provisioning the default?

Chris Friesen chris.friesen at windriver.com
Tue Sep 15 17:00:23 UTC 2015

I'm currently trying to work around an issue where activating LVM snapshots 
created through cinder takes potentially a long time.  (Linearly related to the 
amount of data that differs between the original volume and the snapshot.)  On 
one system I tested it took about one minute per 25GB of data, so the worst-case 
boot delay can become significant.

According to Zdenek Kabelac on the LVM mailing list, LVM snapshots were not 
intended to be kept around indefinitely, they were supposed to be used only 
until the backup was taken and then deleted.  He recommends using thin 
provisioning for long-lived snapshots due to differences in how the metadata is 
maintained.  (He also says he's heard reports of volume activation taking half 
an hour, which is clearly crazy when instances are waiting to access their volumes.)

Given the above, is there any reason why we couldn't make thin provisioning the 


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