Comment about stability
RAID-1 or RAID-5?
"3 1TB disks in an md based raid1 yields a /dev/md0 with 1TB free space and the ability to safely loose 2 disks without losing data. 3 1TB disks in a btrfs volume with data=raid1 will allow the storage of approximately 1.5TB of data before reporting full. Only 1 disk can safely be lost without losing data."
That sounds more like some kind of weird, inefficient RAID-5 arrangement than RAID-1. I don't know btrfs enough to say it's wrong, but I know RAID-1 enough to question it?
- See btrfs wiki:
- btrfs combines all the drives into a storage pool first, and then duplicates the chunks as file data is created. RAID-1 is defined currently as "2 copies of all the data on different disks". This differs from MD-RAID and dmraid, in that those make exactly n copies for n disks. In a btrfs RAID-1 on 3 1TB drives we get 1.5TB of usable data. Because each block is only copied to 2 drives, writing a given block only requires exactly 2 drives spin up, reading requires only 1 drive to spinup.
- -- Karol (talk) 15:59, 17 June 2013 (UTC)
btrfs with fsck hook and fstab pass
Apparently one does not need to have a btrfs partition fscked on boot, so there should be a '0' for 'pass' in the fstab for any btrfs partion. I had relatively slow boot ups with a pass of '1' (btrfs was root)
the genfstab script puts a '1' in for 'pass' by default