I'm using OpenSolaris with ZFS as a backup server.  I copy all my data from 
various sources onto the OpenSolaris server daily, and run a snapshot at the 
end of each backup.  Using gzip-1 compression, mount -F smbfs, and the 
--in-place and --no-whole-file switches for rsync, I get efficient space usage, 
only storing the blocks that changed each day.  This way, I have a backup 
server containing all backups for all days going back effectively indefinitely. 
 Works great.

Of course, I also want to have something that can be rotated and/or taken 
offsite.  What I've done is use an internal drive in the backup server to 
actually receive and store all the backups and snapshots themselves.  Then at 
the end of the actual backup I run a snapshot, and then do a zfs send -R of my 
backup pool and all its snapshots to an external drive.  Not being able to 
trust what's on the drive (its contents could possibly have changed since last 
time I used it, and I want every snapshot on every external drive), I wipe the 
external drive clean and then have it receive the full contents of the 
non-incremental zfs send -R backuppool I mentioned above.

This works.  However, it's painfully slow.  I get the impression that zfs is 
de-compressing and then re-compressing the data instead of transferring it in 
its compressed state, and then when the incrementals start copying over (the 
snapshots themselves), it gets drastically slower.  The whole process works, 
but I'm thinking that when I start getting too many snapshots, it won't finish 
overnight and will run into the next day.

I don't want to just copy over the contents of my most recent snapshot on my 
backup server to the external drive then run a snapshot on the external drive, 
because I'd like each external drive to contain ALL the snapshots from the 
internal drive.

Is there any way to speed up a compressed zfs send -R?  Or is there some other 
way to approach this?  Maybe some way to do a bit-level clone of the internal 
drive to the external drive (the internal backup drive is not the same as the 
OS drive, so it could be unmounted), or SNDR replication or something?

Thanks!
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