[Discuss] btrfs

[Derek Atkins]

Dan Ritter <dsr at randomstring.org> writes:

> 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?

I presume this is also true of RAID-10 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.  
> +++

If you add new disks to an existing array (to grow the array) will it
rebalance the stripes across the new disks?  If so, will it do it
automatically or does it require a user process to rebalance?  (Note
that rebalancing slowly is fine for my usage, provided it's a live
rebalance).   I've a similar question about replacing a disk with a
larger one -- will it properly rebalance?

> -dsr-

-derek

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
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