I use mirrors instead of the RAID-Z because I think the mirrors give you a lot more flexibility. For example, if I have two internal hard disks that are mirroring each other and I want to back up all of my data on an external hard drive, all I have to do is plug in a USB hard drive that is the same size as the internal hard drives and add the USB hard drive as a "third mirrored drive" in the zpool. Then once it's done resilvering (mirroring) the data on the third drive, I can remove it from the USB drive from the zpool and I have an exact block-by-block copy of the orignal internal drive.
Normally you have to buy a thousand dollar enterprise utility like "Acronis" to clone drives like this, but ZFS is easy and it lets you clone drives for free!!! This is the best way IMO to literally back up everything in an entire system in less than an hour. And if you have another computer somewhere else with the exact same hardware as the computer that had the internal drive that you mirrored (and you installed GRUB on the external USB drive), then you can boot up your second computer from the external USB drive and and zpool mirror the internal drive in that computer from the external USB drive and suddenly you've cloned your entire computer including your operating sytem, your configuration files, all your data, everything is there. -- This message posted from opensolaris.org
