Re: multiple device usage

Yan Zheng
2008-12-29T15:16:33Z

2008/12/29 Chris Samuel <chris@csamuel.org>:
> Hello Yan,
>
> On Mon, 29 Dec 2008 11:33:18 pm Yan Zheng wrote:
>
>> 2008/12/29 Chris Samuel <chris@csamuel.org>:
>>
>> > 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.
>>
>> The rebalancing moves data/metadata to newly created chunks. If there
>> are two devices, the new chunks will be set up as RAID-1 by default.
>
> Very interesting! I didn't realise that - I was presuming that the
> BTRFS_BLOCK_GROUP_RAID1 ioctl needed to be passed through (as at mkfs time) to
> change it into a RAID1 array.
>

See __btrfs_reserve_extent and __btrfs_alloc_chunk. There is a mistake in
my previous reply. Only metadata chunks are set up as RAID-1 by default
when there are two devices.

Regards
Yan Zheng