On Tue, 19 Jan 2016 09:33:03 PM Chris Samuel via luv-main wrote:
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'.
That's great news! Still no equivalent to copies=3 though...
# 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.
If you had a cryptsetup device on the SSD then it would be unable to remap the blocks as the block address goes into the encryption calculation.
# 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*.
That depends on what you are doing. I have a collection of 3TB disks that I use for backup which each have between 20 and 100 bad sectors. I run them with BTRFS RAID-1 across 2 partitions and haven't had a problem with them. <100 bad sectors out of 3TB of disk space isn't much and as long as the number of bad sectors doesn't increase dramatically it works OK. The probability of one of those drives failing significantly is greater than the probability for a drive with no bad sectors. But I think it's still lower than the probability of me dropping one of those drives while carrying it around. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/