The ZFS On-Disk specification and other ZFS documentation describe the labeling
scheme used for the vdevs that comprise a ZFS pool. A label entry contains,
among other things, an array of uberblocks, one of which will point to the
active object set of the pool it is a part of at a given instant (according to
documentation, the active uberblock for a given pool could be located in the
uberblock array of any vdev participating in the pool at a given instant, and
is subject to relocation from vdev to vdev as the uberblock for the pool is
recreated in an update). Recreation of the active uberblock would occur, for
example, if we took a snapshot of the pool and changes were then made anywhere
in the pool. Since a new uberblock is required in this snapshot scenario, and
since it appears that the uberblocks are treated as a kind of circular list
across vdevs, it seems to me that the number of available snapshots we could
have of a pool at any given instant would be strictly limited to the number of
available uberblocks in the vdevs of the pool (128 uberblocks per vdev, if I
have that straight). Is this truly the case or am I missing something here ?
This message posted from opensolaris.org
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
