we use filerview to delete multiple snapshots.
On 11/6/05, Chris Thompson cet1@cus.cam.ac.uk wrote:
jeremyw@al.com.au (Jeremy Webber) writes:
I am wondering what is the best order to delete multiple snapshots - oldest first or newest first?
I have assumed that deleting the oldest first will result in less copying of blocks between snapshots, but am wondering if this assumption is correct?
My specific platform is a FAS960 running DataOnTAP 6.5.3P3 but I'm hoping that the answer to this isn't version specific!
There is no "copying of blocks" involved in deleting a snapshot (and it shows some fundamental misapprehensions about ONTAP / WAFL to imagine that there might be). Essentially, the blocks allocated within the snapshot have a reference count decremented, and those for which the count reaches zero become available for re-allocation.
There is some I/O involved in updating the allocation maps, but the only useful advice here is "delete multiple snapshots simultaneously if possible, so that only a single pass updating the maps is required". Unfortunately, the "snap delete" command only allows deletion of one snapshot per invocation, but if they are issued fast enough the resulting passes over the allocation maps do get merged. But all this is a second-order effect.
-- Chris Thompson Email: cet1@cam.ac.uk