Just an additional thought: You can of course mirror vol0 (your 'root + data' volume) from Filer A to vol1 on Filer B as Stephen states.
You can then, if you wish, mirror the reverse as well - in other words, have another vol1 on Filer A, & mirror Filer B's 'root + data' to it.
I know you never have enough to read ;-) so for an overview of the SnapMirror (& SnapRestore) functionality, you might want to take a look at http://www.netapp.com/tech_library/3043.html. The NOW site has a more in-depth operational guide at http://now.netapp.com/NOW/knowledge/docs/olio/guides/TR3073.shtml.
(& as always, the SAG is a good reference point for how-to information ;-)
Cheers Mike
First, ALL of a snapmirrored volume is mirrored. There is no way to make it finer-grained, or to make it exclude certain files or directories.
Let's say you have machines A and B.
A has one volume: vol0. vol0 has 7 disks and is the root volume. Its /etc files are used for machine configuration.
B has two volumes: vol0 and vol1. vol0 has 2 disks and is the root volume. Its /etc files are used for machine configuration. vol1 has 7 disks and is a snapmirror of A:vol0. It is only readable, and its /etc files are NOT used for machine configuration, unless you break the mirror, make it writeable, and make it the root volume.
So, I don't think you need to be too worried about the mirroring of /etc. However, you still would need 2 more disks on B:vol1 to be able to mirror A:vol0 to it.
Stephen Manley Data Availability and Management Set-Up Reliever