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docs: old missing features are not missing any more

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The extent scan mode has been implemented (partially, but close enough
to win benchmarks).

New features include several nuisance dedupe countermeasures.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell 2023-02-25 03:13:23 -05:00
parent 25f7ced27b
commit d5a6c30623
1 changed files with 6 additions and 12 deletions
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docs/missing.md
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@ -15,16 +15,9 @@ specific files (patches welcome).
* PREALLOC extents and extents containing blocks filled with zeros will
be replaced by holes. There is no way to turn this off.
* Consecutive runs of duplicate blocks that are less than 12K in length
can take 30% of the processing time while saving only 3% of the disk
space. There should be an option to just not bother with those, but it's
complicated by the btrfs requirement to always dedupe complete extents.
* There is a lot of duplicate reading of blocks in snapshots. bees will
scan all snapshots at close to the same time to try to get better
performance by caching, but really fixing this requires rewriting the
crawler to scan the btrfs extent tree directly instead of the subvol
FS trees.
* The fundamental unit of deduplication is the extent _reference_, when
it should be the _extent_ itself. This is an architectural limitation
that results in excess reads of extent data, even in the Extent scan mode.
* Block reads are currently more allocation- and CPU-intensive than they
should be, especially for filesystems on SSD where the IO overhead is
@ -33,8 +26,9 @@ much smaller. This is a problem for CPU-power-constrained environments
* bees can currently fragment extents when required to remove duplicate
blocks, but has no defragmentation capability yet. When possible, bees
will attempt to work with existing extent boundaries, but it will not
aggregate blocks together from multiple extents to create larger ones.
will attempt to work with existing extent boundaries and choose the
largest fragments available, but it will not aggregate blocks together
from multiple extents to create larger ones.
* When bees fragments an extent, the copied data is compressed. There
is currently no way (other than by modifying the source) to select a