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Update mkdwarfs man page

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Marcus Holland-Moritz 2021-04-04 17:37:51 +02:00
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@ -75,6 +75,54 @@ Most other options are concerned with compression tuning:
individual filesystem blocks in the background. Ordering, segmenting
and block building are, again, single-threaded and run independently.
* `-B`, `--max-lookback-blocks=`*value*:
Specify how many of the most recent blocks to scan for duplicate segments.
By default, only the current block will be scanned. The larger this number,
the more duplicate segments will likely be found, which may further improve
compression. Impact on compression speed is minimal, but this could cause
resulting filesystem to be slightly less efficient to use, as single small
files can now potentially span multiple filesystem blocks. Passing `-B0`
will completely disable duplicate segment search.
* `-W`, `--window-size=`*value*:
Window size of cyclic hash used for segmenting. This is again an exponent
to a base of two. Cyclic hashes are used by `mkdwarfs` for finding
identical segments across multiple files. This is done on top of duplicate
file detection. If a reasonable amount of duplicate segments is found,
this means less blocks will be used in the filesystem and potentially
less memory will be used when accessing the filesystem. It doesn't
necessarily mean that the filesystem will be much smaller, as this removes
redundany that cannot be exploited by the block compression any longer.
But it shouldn't make the resulting filesystem any bigger. This option
is used along with `--window-step` to determine how extensive this
segment search will be. The smaller the window sizes, the more segments
will obviously be found. However, this also means files will become more
fragmented and thus the filesystem can be slower to use and metadata
size will grow. Passing `-W0` will completely disable duplicate segment
search.
* `-w`, `--window-step=`*value*:
This option specifies how often cyclic hash values are stored for lookup.
It is specified relative to the window size, as a base-2 exponent that
divides the window size. To give a concrete example, if `--window-size=16`
and `--window-step=1`, then a cyclic hash across 65536 bytes will be stored
at every 32768 bytes of input data. If `--window-step=2`, then a hash value
will be stored at every 16384 bytes. This means that not every possible
65536-byte duplicate segment will be detected, but it is guaranteed that
all duplicate segments of (`window_size` + `window_step`) bytes or more
will be detected (unless they span across block boundaries, of course).
If you use a larger value for this option, the increments become *smaller*,
and `mkdwarfs` will be slightly slower and use more memory.
* `--bloom-filter-size`=*value*:
The segmenting algorithm uses a bloom filter to determine quickly if
there is *no* match at a given position. This will filter out more than
90% of bad matches quickly with the default bloom filter size. The default
is pretty much where the sweet spot lies. If you have copious amounts of
RAM and CPU power, feel free to increase this by one or two and you *might*
be able to see some improvement. If you're tight on memory, then decreasing
this will potentially save a few MiBs.
* `-L`, `--memory-limit=`*value*:
Approximately how much memory you want `mkdwarfs` to use during filesystem
creation. Note that currently this will only affect the block manager
@ -156,6 +204,11 @@ Most other options are concerned with compression tuning:
reduce the size of the file system. You can pass either a unix time stamp
or `now`.
* `--keep-all-times`:
As of release 0.3.0, by default, `mkdwarfs` will only save the contents of
the `mtime` field in order to save metadata space. If you want to save
`atime` and `ctime` as well, use this option.
* `--time-resolution=`*sec*|`sec`|`min`|`hour`|`day`:
Specify the resolution with which time stamps are stored. By default,
time stamps are stored with second resolution. You can specify "odd"
@ -163,11 +216,6 @@ Most other options are concerned with compression tuning:
entirely possible. Moving from second to minute resolution, for example,
will save roughly 6 bits per file system entry in the metadata block.
* `--keep-all-times`:
As of release 0.3.0, by default, `mkdwarfs` will only save the contents of
the `mtime` field in order to save metadata space. If you want to save
`atime` and `ctime` as well, use this option.
* `--order=none`|`path`|`similarity`|`nilsimsa`[`:`*limit*[`:`*depth*[`:`*mindepth*]]]|`script`:
The order in which inodes will be written to the file system. Choosing `none`,
the inodes will be stored in the order in which they are discovered. With
@ -195,54 +243,6 @@ Most other options are concerned with compression tuning:
Last but not least, if scripting support is built into `mkdwarfs`, you can
choose `script` to let the script determine the order.
* `-W`, `--window-size=`*value*:
Window size of cyclic hash used for segmenting. This is again an exponent
to a base of two. Cyclic hashes are used by `mkdwarfs` for finding
identical segments across multiple files. This is done on top of duplicate
file detection. If a reasonable amount of duplicate segments is found,
this means less blocks will be used in the filesystem and potentially
less memory will be used when accessing the filesystem. It doesn't
necessarily mean that the filesystem will be much smaller, as this removes
redundany that cannot be exploited by the block compression any longer.
But it shouldn't make the resulting filesystem any bigger. This option
is used along with `--window-step` to determine how extensive this
segment search will be. The smaller the window sizes, the more segments
will obviously be found. However, this also means files will become more
fragmented and thus the filesystem can be slower to use and metadata
size will grow. Passing `-W0` will completely disable duplicate segment
search.
* `--window-step=`*value*:
This option specifies how often cyclic hash values are stored for lookup.
It is specified relative to the window size, as a base-2 exponent that
divides the window size. To give a concrete example, if `--window-size=16`
and `--window-step=1`, then a cyclic hash across 65536 bytes will be stored
at every 32768 bytes of input data. If `--window-step=2`, then a hash value
will be stored at every 16384 bytes. This means that not every possible
65536-byte duplicate segment will be detected, but it is guaranteed that
all duplicate segments of (`window_size` + `window_step`) bytes or more
will be detected (unless they span across block boundaries, of course).
If you use a larger value for this option, the increments become *smaller*,
and `mkdwarfs` will be slightly slower and use more memory.
* `-B`, `--max-lookback-blocks=`*value*:
Specify how many of the most recent blocks to scan for duplicate segments.
By default, only the current block will be scanned. The larger this number,
the more duplicate segments will likely be found, which may further improve
compression. Impact on compression speed is minimal, but this could cause
resulting filesystem to be slightly less efficient to use, as single small
files can now potentially span multiple filesystem blocks. Passing `-B0`
will completely disable duplicate segment search.
* `--bloom-filter-size`=*value*:
The segmenting algorithm uses a bloom filter to determine quickly if
there is *no* match at a given position. This will filter out more than
90% of bad matches quickly with the default bloom filter size. The default
is pretty much where the sweet spot lies. If you have copious amounts of
RAM and CPU power, feel free to increase this by one or two and you *might*
be able to see some improvement. If you're tight on memory, then decreasing
this will potentially save a few MiBs.
* `--remove-empty-dirs`:
Removes all empty directories from the output file system, recursively.
This is particularly useful when using scripts that filter out a lot of