Nicolas,
On Fri, Mar 06, 2009 at 10:05:46AM -0700, Neil Perrin wrote:
On 03/06/09 08:10, Jim Dunham wrote:
A simple test I performed to verify this, was to append to a ZFS
file
(no synchronous filesystem options being set) a series of blocks
with a
block order pattern contained within. At some random point in this
process, I took a ZFS snapshot, immediately dropped SNDR into
logging
mode. When importing the ZFS storage pool on the SNDR remote host, I
could see the ZFS snapshot just taken, but neither the snapshot
version
of the file, or the file itself contained all of the data previously
written to it.
That seems like a bug in ZFS to me. A snapshot ought to contain all
data
that has been written (whether synchronous or asynchronous) prior
to the
snapshot.
Wouldn't one have to quiesce (export) the pool on the primary before
importing it on the secondary?
No. ZFS is always on-disk consistent, so as long as SNDR is in logging
mode, zpool import will work on the secondary node.
Or does SNDR detect suitable checkpoints
using, say, ZFS's cache flush commands?
SNDR is totally volume and filesystem agnostic. It does not know if
ZFS, UFS, VxFS, Oracle, Sybase, some application, is writing to the
SNDR primary volume. It also does not know if the volumes being
replicated are JBODs, RAID-1, RAID-5, RaidZ, RaidZ2.
Very simplistically, SNDR replicates write I/Os made to the SNDR
primary volume, to the SNDR secondary volume. Unfortunately, SNDR is
nowhere as simple to use as ZFS's send / receive.
- Jim
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