Daniel Denson wrote:
> i think you missed the point on sending zfs snapshots.  *if* the remote 
> filesystem is in sync with the snapshot you have then it should work, 
> but what if that is not the case?

Don't do the next one until the previous has succeeded.  All you need is 
a status returned for the transfer and some simple scripting for that.

> if the remote filesystem is not 
> synced with any specific snapshot, then there is no base level target to 
> snapshot from so the new smaller snapshot cannot be created because 
> common sync point is not known.

Don't discard your previous snapshots at either end until the update 
succeeds.

> you would first have to make sure that 
> the remote filesystem matched a snapshot on the local system and then 
> proceed if it does, if it does not then what?  run a 100+GB complete 
> sync over a 1.5Mb link?

Don't let that happen.  If an incremental doesn't succeed, revert the 
target and start that update over again.

> there is the problem, what the remote system 
> falls out of sync because of a deleted snapshot or missed sync?  how 
> will you check to see if the remote filesystem and local snapshot are 
> the same?

If the incremental update status says it succeeds, I'd expect it to have 
actually succeeded.  I thought that zfs had its own internal 
checksumming concepts to ensure that it is consistent.  In any case, if 
you felt you had to do a check you could probably do an 'rsync -n' on 
the pool and each pc directory separately.  You don't need to 
reconstruct the hardlinks in this case, just verify that the contents 
exist and match - so you don't take the hit of having to get all the 
filenames loaded in one run.

> I think the intent of the zfs send is just to migrate a filesystem from 
> one system to another.

Then why would it have an incremental mode?  The real question is 
whether it is efficient enough in handling hardlinks to make it worth 
scripting the updates to make sure the updates are applied consistently.

> as far as rsync in concerned, i think that you need to have a ton of ram and 
> a fast CPU to make large fileset transfers work, which I have.  I doubt a 1GB 
> p3 1Ghz is going to cut it.

Hmmm, you probably need a 64-bit OS too, so you can use that ram in one 
process.

-- 
   Les Mikesell
    lesmikesell AT gmail DOT com


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