On 10 December 2014 at 13:06, Russell Coker <russell@coker.com.au> wrote:
On Wed, 10 Dec 2014, Toby Corkindale <toby@dryft.net> wrote:
Let's say I want to have 2TB of storage. In that case, I'd purchase two 2TB drives, mirror them in btrfs, done.[1] mkfs.btrfs -m raid1 -d raid1 /dev/disk/by-id/foo1 /dev/disk/by-id/foo2
Actually buy at least 3TB disks. The MSY prices are $92 and $123 [snip]
I was really just using the size as an arbitrary amount for example's sake. I haven't looked recently to see what sort of sizes are good value, but I would expect people using this advice to do so, yes.
Time goes by, the amount of data I'm collecting ramps up hugely, I need more space. So, I'd buy a couple of 4TB drives, and add them to the pool and then perhaps rebalance: btrfs device add /dev/disk/by-id/foo3 /mnt btrfs device add /dev/disk/by-id/foo4 /mnt btrfs balance start /mnt
Later, I'd remove the original drives as they were getting old, and probably look at replacing them with bigger drives. btrfs device delete /dev/disk/by-id/foo1 /mnt btrfs device delete /dev/disk/by-id/foo2 /mnt
Note that "btrfs replace" is MUCH faster than a balance or delete operation.
Thanks Russell, that's interesting to know. Might not be an option for someone if they only have four or five ports, but sounds good if you do have a spare.
Another possibility is to use an old PC with a few disks in a RAID-5 or RAID-6 array for local backup. I've been considering getting a large tower PC filled with old disks (~1TB capacity) in a BTRFS RAID-5 configuration for local backup. The noise and heat of all the disks wouldn't matter as I'd only turn it on when doing a backup.
You start getting into higher failure rates there -- old drives, lots of them, frequently getting spun up and down..