On 09/15/2015 04:56 PM, yang, xing wrote: > Hi Eric, > > Regarding the default max_over_subscription_ratio, I initially set the > default to 1 while working on oversubscription, and changed it to 2 after > getting review comments. After it was merged, I got feedback that 2 is > too small and 20 is more appropriated, so I changed it to 20. So it looks > like we can¹t find a default value that makes everyone happy. >
I'm curious about how this is used in real-world deployments. Are we making the assumption that the admin has some external monitoring configured to send alarms if the storage is nearing capacity? > If we can decide what is the best default value for LVM, we can change the > default max_over_subscription_ratio, but we should also allow other > drivers to specify a different config option if a different default value > is more appropriate for them. This sounds like a good idea, I'm just not sure how to structure it yet without creating a very confusing set of config options. > On 9/15/15, 1:38 PM, "Eric Harney" <ehar...@redhat.com> wrote: > >> On 09/15/2015 01:00 PM, Chris Friesen wrote: >>> 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 default? >>> >> >> >> My intention is to move toward thin-provisioned LVM as the default -- it >> is definitely better suited to our use of LVM. Previously this was less >> easy, since some older Ubuntu platforms didn't support it, but in >> Liberty we added the ability to specify lvm_type = "auto" [1] to use >> thin if it is supported on the platform. >> >> The other issue preventing using thin by default is that we default the >> max oversubscription ratio to 20. IMO that isn't a safe thing to do for >> the reference implementation, since it means that people who deploy >> Cinder LVM on smaller storage configurations can easily fill up their >> volume group and have things grind to halt. I think we want something >> closer to the semantics of thick LVM for the default case. >> >> We haven't thought through a reasonable migration strategy for how to >> handle that. I'm not sure we can change the default oversubscription >> ratio without breaking deployments using other drivers. (Maybe I'm >> wrong about this?) >> >> If we sort out that issue, I don't see any reason we can't switch over >> in Mitaka. >> >> [1] https://review.openstack.org/#/c/104653/ >> >> __________________________________________________________________________ >> OpenStack Development Mailing List (not for usage questions) >> Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe >> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev > > > __________________________________________________________________________ > OpenStack Development Mailing List (not for usage questions) > Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev > __________________________________________________________________________ OpenStack Development Mailing List (not for usage questions) Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
