Re: multiple device usage

[Chris Samuel <chris@csamuel.org>]

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On Sat, 27 Dec 2008 5:45:42 pm Chris Samuel wrote:

> I'll add two questions that're not answered by the Wiki too.. :-)

Looking at the source implies to me:

> 1) If you add a second disk to an existing btrfs filesystem, can you get it
> to set it up as a RAID-1 arrangement rather than just rebalancing the
> metadata and then striping ?

No, you can't, the data stripe numbers seem to be set at mkfs time.

The rebalancing code does appear (from a naive read of the code) to be able to 
rebalance over stripes, but I have no idea if the disk format currently 
supports changing that on the fly.

> 2) With the concerns that people have about SSD reliability (hi Val :-) !)
> would it make sense to set up two equal sized partitions on the SSD and use
> RAID-1 across them, or can you tell btrfs to keep multiple copies of the
> data, a la ZFS ?

Again it would appear that you need to have two partitions and that btrfs 
cannot (at present) keep multiple data stripes on the same partition.

Could someone who actually knows the code to comment on whether my inferences 
are accurate or not please ?  :-)

cheers,
Chris
-- 
 Chris Samuel  :  http://www.csamuel.org/  :  Melbourne, VIC

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