Is it possible with a raid10 filesystem to control which devices contain which halves of the mirror? I'll give you an example of why I'm asking. I've previously build raid10 volumes on HP-UX. HP's implementation of LVM includes a feature called Physical Volume Groups. Disks can be included in an LVM VG and then bunched into PVGs so that when creating a mirrored LV the mirror is split across PVGs. On systems with dual raid cards this has allowed me to put all the disks attached to one raid card in one PVG and disks attached to the other in a second PVG. The result is that I/O to a mirrored LV gets split evenly between both raid cards, doubling up the available bandwidth. In addition, it protects my LVs from a complete single raid controller failure. To achieve the same result on Linux today I must first use md to mirror devices across raid cards before adding the md devices to an LVM VG. Then I create LVs as normal and leave the mirroring down to md to sort out. It's a perfectly workable solution, but given that the ultimate goal of btrfs is to make md redundant, will we be able to achieve the same result in btrfs somehow? The wiki (linked in the article) doesn't hint at this. Thanks. »