On Tue, 12 Jan 2016 04:16:27 PM Russell Coker via luv-main wrote: > BTRFS doesn't support duplicate data blocks (in any normal or desirable > configuration) unlike ZFS which has the copies= configuration.
David Sterba just released btrfs-progs 4.4 which has a new feature: # * mkfs.btrfs --data dup # # People asked about duplicating data on a single device for a long time. # There are no technical obstacles preventing that, so it got enabled with # a warning about potential dangers when the device will not do the # duplicated copies. # # See mkfs.btrfs section 'DUP PROFILES ON A SINGLE DEVICE'. The referenced manual page says: https://git.kernel.org/cgit/linux/kernel/git/kdave/btrfs-progs.git/tree/Documentation/mkfs.btrfs.asciidoc # DUP PROFILES ON A SINGLE DEVICE # ------------------------------- # # The mkfs utility will let the user create a filesystem with profiles that write # the logical blocks to 2 physical locations. Whether there are really 2 # physical copies highly depends on the underlying device type. # # For example, a SSD drive can remap the blocks internally to a single copy thus # deduplicating them. This negates the purpose of increased redunancy and just # wastes space. # # The duplicated data/metadata may still be useful to statistically improve the # chances on a device that might perform some internal optimizations. The actual # details are not usually disclosed by vendors. As another example, the widely # used USB flash or SD cards use a translation layer. The data lifetime may # be affected by frequent plugging. The memory cells could get damaged, hopefully # not destroying both copies of particular data. # # The traditional rotational hard drives usually fail at the sector level. # # In any case, a device that starts to misbehave and repairs from the DUP copy # should be replaced! *DUP is not backup*. -- Chris Samuel : http://www.csamuel.org/ : Melbourne, VIC _______________________________________________ luv-main mailing list luv-main@luv.asn.au http://lists.luv.asn.au/listinfo/luv-main
