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Update mkdwarfs man page

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Marcus Holland-Moritz 2020-12-10 21:23:12 +01:00
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@ -94,9 +94,9 @@ Most other options are concerned with compression tuning:
The compression algorithm and configuration used for the metadata.
Takes the same arguments as `--compression` above. The metadata has been
optimized for very little redundancy and leaving it uncompressed, the
default for all levels below 8, has the benefit that it can be mapped
to memory and used directly. This significantly improves mount time for
large file systems compared to e.g. an lzma compressed metadata block.
default for all levels below 7, has the benefit that it can be mapped
to memory and used directly. This improves mount time for large file
systems compared to e.g. an lzma compressed metadata block.
* `--recompress`:
Take an existing DwarFS filesystem and recompress it using a different
@ -224,18 +224,17 @@ find that it's much faster with zstd.
### Block, Schema and Metadata Compression
DwarFS filesystems consist of three distinct parts of data. Many blocks,
which store actual file data and are decompressed on demand, as well as
one schema and one metadata section. The schema is tiny, typically less
than 1000 bytes, and holds the details for how to interpret the metadata.
The schema needs to be read into memory once and is subsequently never
accessed again. The metadata itself is usually not compressed, although
it can be if you want to squeeze a few more kilobytes out of the file
system. If it is compressed, it will be fully decompressed into memory.
Otherwise, the metadata part of the file will simply be mapped into memory.
The main difference is that compressed metadata, which being smaller, will
potentially consume more memory and it will definitely take longer to
mount the filesystem initially.
DwarFS filesystems consist of three distinct parts of data: A potentially
large number of blocks, which store actual file data and are decompressed
on demand, as well as one schema and one metadata section. The schema is
tiny, typically less than 1000 bytes, and holds the details for how to
interpret the metadata. The schema needs to be read into memory once and
is subsequently never accessed again. The metadata itself is compressed
by default, but it doesn't have to be. Actually, if you drop the compression
level from 7 (the default) to 6, the only difference is that the metadata
is left uncompressed. This can be useful if mounting speed of the file
system is important, as the uncompressed metadata part of the file can
then simply be mapped into memory.
## AUTHOR