[OmniOS-discuss] Auto snapshots?

[Basil Crow]

On Tue, Apr 23, 2013 at 7:40 AM, Eric Sproul <esproul at omniti.com> wrote:
> But beyond those specifics, in the case where ZFS is providing a
> backing store for what are seen as block devices by the ESXi guests,
> you probably don't want blind ZFS snapshotting for the simple reason
> that ZFS alone cannot ensure that the on-disk state of a given virtual
> disk is consistent from the guest's viewpoint.  ZFS will happily
> snapshot the filesystem on which the virtual disk file resides, but if
> there are in-flight transactions in the guest to the filesystem backed
> by that virtual disk file, the state represented by the snapshot may
> be inconsistent.  You need some way to coordinate quiescing the guests
> whose storage sits on the filesystem you want to snapshot, to make
> sure their buffer caches are flushed out prior to the snapshot.  Maybe
> someone on the list who does this can pipe up with specific techniques
> in the VMware universe.

Here at Delphix, we attempt to sync pending I/O by running
/usr/sbin/sync in the guest OS with VMware Tools before taking the
snapshot. It works well enough for our use case.

Basil