On Tue, 26 Feb 2013 11:02:35 -0500 Derek Atkins <warl...@mit.edu> wrote:
> Thank you for the detailed description. Could you give (or point me > to) a brief description of how ZFS's RAID differs from these > configurations? The basic difference is that ZFS mirrors device blocks while Btrfs replicates file extents. zpools (ZFS device pools) are built from vdevs. A vdev is one or more physical devices that are bonded together. Mirroring and parity (RAID-Z) occur here within the vdevs. In a mirrored configuration, all devices in the vdev are identical replicas less housekeeping information. In a parity configuration, data written to one device has parity information written to other devices in the vdev. Striping occurs automatically when two or more vdevs are assigned to a zpool. Again, the difference becomes evident when you compare three device mirrored vdevs to three device Btrfs raid1. Given three devices with capacities of 1TB, 2TB and 3TB. The ZFS vdev has a capacity of 1TB. The Btrfs volume has a capacity of 3TB. Another difference is that ZFS really, really wants to be the RAID system to the point where ZFS best practices recommend setting any RAID controller to JBOD. On the other hand, Btrfs is quite happy sitting on top of hardware RAID volumes. -- Rich P. _______________________________________________ Discuss mailing list Discuss@blu.org http://lists.blu.org/mailman/listinfo/discuss
