sridhar surampudi wrote:
Hi Darren,
In shot I am looking a way to freeze and thaw for zfs file system so that for
harware snapshot, i can do
1. run zfs freeze
2. run hardware snapshot on devices belongs to the zpool where the given file system is residing.
3. run zfs thaw
Unlike other filesystems, ZFS is always consistent on disk, so there's
no need to freeze a zpool to take a hardware snapshot. The hardware
snapshot will effectively contain all transactions up to the last
transaction group commit, plus all synchronous transactions up to the
hardware snapshot. If you want to be sure that all transactions up to a
certain point in time are included (for the sake of an application's
data), take a ZFS snapshot (which will force a TXG commit), and then
take the hardware snapshot. You will not be able to access the hardware
snapshot from the system which has the original zpool mounted, because
the two zpools will have the same pool GUID (there's an RFE outstanding
on fixing this).
The one thing you do need to be careful of is, that with a multi-disk
zpool, the hardware snapshot is taken at an identical point in time
across all the disks in the zpool. This functionality is usually an
extra-charge option in Enterprise storage systems. If the hardware
snapshots are staggered across multiple disks, all bets are off,
although if you take a zfs snapshot immediately beforehand and you test
import/scrub the hardware snapshot (on a different system) immediately
(so you can repeat the hardware snapshot again if it fails), maybe you
will be lucky.
The right way to do this with zfs is to send/recv the datasets to a
fresh zpool, or (S10 Update 9) to create an extra zpool mirror and then
split it off with zpool split.
--
Andrew Gabriel
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