If I remember correctly, it takes quite a while for the "zpool attach" command to run because it's taking all the data on one drive and copying it over to another drive (took a quite a while in my case because I was mirroring 700 gig drives). Also, expect your hard drive's read and write response time to slow while this is going on.
The thing that's kind of confusing is that there isn't an obvious progress bar at the command line that shows you how far the "zpool attach" has progressed, so what you need to do is periodically type in this command: zpool status or zpool status -v to see how far the mirroring has progressed. Keep us updated and let us know how it turns out. -- This message posted from opensolaris.org
