Hi,
On 2016-08-25 21:50, Chris Murphy wrote:
It's incidental right now. It's not something controllable or intended
to have enduring mixed profile block groups.
I see. (Kindof)
Such a switch doesn't exist, there's no way to define what files,
directories, or subvolumes, have what profiles.
Well it kind of does - a running balance process seems to have just that
effect, it's just not persistent (and has the side effect of, well,
balancing the existing data).
How does btrfs
find out which raid mode to use when writing new data?
That's kindof an interesting question. If you were to do 'btrfs
balance start -dconvert=single -mconvert=raid1' and very soon after
that do 'btrfs balance cancel' you'll end up with one or a few new
chunks with those profiles. When data is allocated to those chunks,
they will have those profile characteristics. When data is allocated
to old chunks that are still raid0, it will be raid0. The thing is,
you can't really tell or control what data will be placed in what
chunk. So it's plausible that some new data goes in old raid0 chunk,
and some old data goes in new single/raid1 chunks.
I'm not quite familiar with the concept of a chunk here.
Are chunks allocated for new data, or is the unallocated space divided
into chunks, too?
In the former case, when creating a new chunk, does btrfs just look into
a random already existing chunk and copy the raid mode from there?
In the latter case, could you (in theory) change the raid mode of all
empty chunks only?
I know this is not an intended usage scenario; just being curious here.
Thanks!
Gert
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