[Discuss] btrfs

[Dan Ritter]

On Tue, Feb 26, 2013 at 12:44:32AM +0000, Edward Ned Harvey (blu) wrote:
> performance should be approx N-1 disks times a single disk
> Incrementally expandable by adding individual disks?  I know raidz is not.

Yes, and also live-convertible to different raid schemes (albeit
slowly).

>From the faq:

+++
 How much space do I get with unequal devices in RAID-1 mode?

If your largest device is bigger than all of the others put
together, then you will get as much space as all the smaller
devicess added together. Otherwise, you get half of the space of
all of your devices added together.

For example, if you have disks of size 3TB, 1TB, 1TB, your
largest disk is 3TB and the sum of the rest is 2TB. In this
case, your largest disk is bigger than the sum of the rest, and
you will get 2TB of usable space.

If you have disks of size 3TB, 2TB, 2TB, then your largest disk
is 3TB and the sum of the rest of 4TB. In this case, your
largest disk is smaller than the sum of the rest, and you will
get (3+2+2)/2 = 3.5TB of usable space.  
+++

-dsr-