On 09/14/12 22:39, Edward Ned Harvey (opensolarisisdeadlongliveopensolaris) wrote:
From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
boun...@opensolaris.org] On Behalf Of Dave Pooser

Unfortunately I did not realize that zvols require disk space sufficient
to duplicate the zvol, and my zpool wasn't big enough. After a false start
(zpool add is dangerous when low on sleep) I added a 250GB mirror and a
pair of 3GB mirrors to miniraid and was able to successfully snapshot the
zvol: miniraid/RichRAID@exportable

This doesn't make any sense to me.  The snapshot should not take up any 
(significant) space on the sending side.  It's only on the receiving side, 
trying to receive a snapshot, that you require space.  Because it won't clobber 
the existing zvol on the receiving side until the complete new zvol was 
received to clobber it with.

But simply creating the snapshot on the sending side should be no problem.

By default, zvols have reservations equal to their size (so that writes don't fail due to the pool being out of space).

Creating a snapshot in the presence of a reservation requires reserving enough space to overwrite every block on the device.

You can remove or shrink the reservation if you know that the entire device won't be overwritten.

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