On 11/17/2014 07:37 AM, Payes Anand wrote: > This patchset adds virDomainFSFreeze()/virDomainFSThaw() APIs and virsh >> domfsfreeze/domfsthaw commands to enable the users to freeze and thaw >> domain's filesystems cleanly. >> > > Do these API's ( commands ) also push the dirty buffer to the disk, or it > has to be done separately before freezing, to take snapshots. virDomainFSFreeze does whatever the guest agent is wired to do (and the default implementation of qemu-guest-agent has hooks for you to add any additional work around the envelope of freezing your guest's filesystem). There have been other threads on this list on how to add a hook that prepares a database to be frozen, for example. Passing the --quiesce flag to taking a snapshot is just shorthand for triggering the same actions as what you manually control by calling virDomainFSFreeze yourself. > > If we don't specify any mount points, how different is > domfsfreeze/domfsthaw from suspend/resume. Which of them would be better to > take live incremental external snapshots of iSCSI devices. suspend does NOT flush pending guest I/O. It just stops the guest CPUs from making further changes. Taking a snapshot of a suspended guest is NOT going to be consistent in the same way as a snapshot of a guest that has had its filesystems frozen (that is, booting the disks that were copied from the time that a guest was frozen will likely need fsck repair, and will not contain pending I/O transactions that were still held in memory; while booting a disk that was copied while filesystems were frozen should see a fully consistent file system that is not lacking any pending I/O). -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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