On 4/5/20 10:22 AM, Achim Gratz wrote:
Goffredo Baroncelli writes:
This is an RFC; I wrote this patch because I find the idea interesting
even though it adds more complication to the chunk allocator.
The core idea is to store the metadata on the ssd and to leave the data
on the rotational disks. BTRFS looks at the rotational flags to
understand the kind of disks.
My comment really is only about his aspect of your proposal: I would
consider a more general way of introducing a tiering of disks so that
one can discern between slower and faster SSD as well.
This is a further step. I didn't mind to a tiering of fast (NVM ?) and slow
SSD. For that there are some unused fields in the superblock
which can be used.
However now my first concern is if this is
a) really useful
b) I introduced some functional regression
Regarding a), there is an increment of performance; however stacking
btrfs over bcache leads to an even bigger gain; of course stacking
btrfs over bcache complicates the configuration for the raid setup
Regarding b) the only regression that I found is that the logic
behind the allocation of disks in RAID5/RAID6 became more
complex. But I am not sure if this can be called regression.
Regards,
Achim.
BR
G.Baroncelli
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