On Thu, Aug 25, 2016 at 7:21 PM, Marcin MirosÅ?aw <marcin@xxxxxxxx>
wrote:
W dniu 25.08.2016 o 02:03, Christopher James Halse Rogers pisze:
Hi!
On Thu, Aug 25, 2016 at 7:21 AM, marcin@xxxxxxxx wrote:
[...]
Does it means that cache is unavailable and only tiering will be in
bcachefs?
And... How to mount tiered FS? When I pass one device in mount I'm
getting:
bcache: bch_open_as_blockdevs() register_cache_set err
insufficient
devices
Tiering gets you all the advantages of caching, plus you can (with
some
effort) have the combined filesystem size be the sum of the SSD +
HDD
capacities, rather than the capacity be determined solely by the
capacity of the slow tier (this is not currently the case for
bcachefs).
I think that cacheing has at least such advantages over tiering:
- allow fast read and write to files compressed with slow alghoritm
(gzip)
I think this is getting into ā??what should we call this thingā??
arguments. A naive cache is just going to promote the gzipped data to
the fast storage. On the other end, there's nothing much preventing a
sophisticated tiering system from compressing/decompressing as a part
of tier demotion/promotion.
- can be optimized for using SSD drives
It's not clear to me how? Tiering and caching are doing the same sort
of things.
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