Incremental backup using zfs send

[glowkrantz]

So now we have working zfs send on snapshots i.e. level 0 backups. On my test installation that takes 5 LTO 2 tapes and 18 hours.

Any discussions on how to handle incremental backups on zfs?
I have been looking at ways to estimate and have come to the following:
Level 0: good approximation by filesystem referenced count, maybe a little bit low but the error is small. It does not warrant doing a dummy snapshot for level 0 estimations only.
Level 1+: No way to estimate, only way is running
zfs send -i pool/fs@0 pool/fs@1 | wc -c

Any thoughts?

How accurate must the estimate be?

Does amanda do 0 -> 1 -> 2 -> 1 or only 0 -> 1 -> 2 -> 0? I only see the later when running dump. If the later sequence is the only one, it means that only the latest snapshot needs to be kept between backups.

Is level 9 sufficient? On some large filesystems with streaming media, I consistently was doing level 5 to 8 backups when they were UFS and used dump.

Is the snapshot name fixed in the current code or can it be changed to something like pool/fs@amanda.diskname.level i.e. system/usr/local@amanda._usr_local.0, system/usr/local@amanda._usr_local.1 etc?

Unless there is anything that I can test already, I will try and experiment over the weekend and see what I come up with.

/glz