On Tue, Apr 28, 2015 at 2:11 PM, Neil Bothwick <[email protected]> wrote: > On Tue, 28 Apr 2015 13:38:55 -0400, Rich Freeman wrote: > >> > The same is also possible with BTRFS, including built in RAID. RAID5 >> > in btrfs is expermiental, but its RAID1 is like RAID5 in some ways, >> > such as giving the capacity of n-1 disks and tolerating a single disk >> > failure. >> >> btrfs raid5 is still fairly experimental (though now it supports >> recovery) and works more-or-less how you'd expect raid5 to work. >> Raid1 on btrfs gives you the capacity of n/2 and not n-1 disks, > > You're right, I was clearly confused (an oxymoron?) when I wrote that. > > So RAID1 gives less capacity than RAID5 on BTRFS, but it is stable (in > btrfs terms). >
Correct. For drives of identical size and not using compression, I'd expect space use on btrfs to be equivalent to the same raid level on mdadm+lvm+ext4. With mixed drives you will potentially get more space on btrfs, and compression will of course get you more space. As far as data security goes there is a tradeoff. Btrfs is still immature and I seem to have issues with it 1-2 times per year (but I've yet to have unrecoverable data loss). On the other hand, btrfs does do full data checksumming which means you're less likely to lose data due to issues with the physical storage than with mdadm - as with zfs it always checks the checksum and will recover from another disk if possible, and in the event of raid disparity it always knows which (if any) of the copies is right. I'm hopeful that at some point I'll be able to recommend it without reservation. Right now, that isn't entirely the case. I'm still patching the 3.18 kernel series so that it actually mounts my root partition when whatever is causing it to panic (probably also btrfs) does so (the patch is in the queue, but hasn't made it to 3.18 yet for some reason - I believe it has been in the other stable series for a release or two now). -- Rich
