I understand that SV is a backup tool to back up local volumes, through transferring local SS to a remote site. However, are these transferred SS identical to local SS's? In another words, can I copy these transferred SS's back to the local, and restore data from there? If yes, I can then reduce the local SS's, to save local disk space.
"However, are these transferred SS identical to local SS's?"
Identical in what sense? As far as I know a snapshot is a snapshot is a snapshot, though they can be created for different purpose and based on different schedules. That data in the snapshot will of course be dependant on when the snapshot occured.
"In another words, can I copy these transferred SS's back to the local, and restore data from there? "
I think snapvault restore puts the data back in to the 'live' file system. You may be able to transfer that snapshot back via snapmirror or snapvault by specifcing the snapshot name...I've just never needed to do that as typically our restores are partial vs an entire file system.
"I can then reduce the local SS's, to save local disk space."
Keep in mind that snapshots are only 'saving' the changed blocks so it may say you some, but that will really depend on how much data you're creating/deleting during the time period. I can say that when we have SV enabled, we let snapvault manage all the snapshots (snapvault snap shced) and disable the normal snapshot schedules...you certainly don't want them conflicting with each other.
Not exactly in that way, but the data is restorable from the vault. It would depend on how much data you are looking to recover (a few files or the whole volume). But the idea behind SnapVault is that you can reduce the number of snapshots you keep on the primary filer as the snapshot'ed data will be available on the secondary filer (the vault).
You can't add a snaphot back on the source volume, but you can recover the data that was in that snapshot.
A follow-up. In addtion to SV, do people usually also enable the local SnapShots? I know some people they would disable local SS's, and let SV to generate SS's, however, what if I wanted to do a quick restore, then restoring from local SS's will be quick. So, does that make sense, if I keep local SS's for 4 hourly per day, and 2 weekly retention, in addtion to whatever SV policy is?
Yes, we also keep local snapshots but they are all controled by snapvault (snapvault snap sched not snap sched). So for example we may keep 6 hourly and 2 nightly snapshots locally, but everynight we transfer that latest nightly to the snapvault filer. Hope that helps.
The snapshots are the same whether created by 'snap sched' or 'snapvault snap sched' - I just find it easier to keep all the schedules under one command (versus having to look at two different commands and worry about conflicts between the two).