On Sat, Feb 25, 2012 at 4:56 PM, Richard Yao <r...@cs.stonybrook.edu> wrote: > raidz has 3 varieties, which are single parity, double parity and > triple parity. As for reshaping, ZFS is a logical volume manager. You > can set and resize limits on ZFS datasets as you please.
That isn't my understanding as far as raidz reshaping goes. You can create raidz's and add them to a zpool. You can add individual drives/partitions to zpools. You can remove any of these from a zpool at any time and have it move data into other storage areas. However, you can't reshape a raidz. Suppose I have a system with 5x1TB hard drives. They're merged into a single raidz with single-parity, so I have 4TB of space. I want to add one 1TB drive to the array and have 5TB of single-parity storage. As far as I'm aware you can't do that with raidz. What you could do is set up some other 4TB storage area (raidz or otherwise), remove the original raidz, recycle those drives into the new raidz, and then move the data back onto it. However, doing this requires 4TB of storage space. With mdadm you could do this online without the need for additional space as a holding area. ZFS is obviously a capable filesystem, but unless Oracle re-licenses it we'll never see it take off on Linux. For good or bad everybody seems to like the monolithic kernel. Btrfs obviously has a ways to go before it is a viable replacement, but I doubt Oracle would be sinking so much money into it if they intended to ever re-license ZFS. Rich
