Combines the random access indexing idea from tarindexer and then mounts the TAR using fusepy for easy read-only access just like archivemount. In contrast to libarchive, on which archivemount is based, random access and true seeking is supported.
Other capabilities:
- Recursive Mounting: Ratarmount will also mount TARs inside TARs inside TARs, ... recursively into folders of the same name, which is useful for the 1.31TB ImageNet data set.
- Mount Compressed Files: You may also mount files with one of the supported compression schemes. Even if these files do not contain a TAR, you can leverage ratarmount's true seeking capabilities when opening the mounted uncompressed view of such a file.
- Read-Only Bind Mounting: Folders may be mounted read-only to other folders for usecases like merging a backup TAR with newer versions of those files residing in a normal folder.
- Union Mounting: Multiple TARs, compressed files, and bind mounted folders can be mounted under the same mountpoint.
Compressions supported for random access:
- BZip2 as provided by indexed_bzip2 as a backend, which is a refactored and extended version of bzcat from toybox. See also the reverse engineered specification.
- Gzip as provided by indexed_gzip by Paul McCarthy. See also RFC1952.
- Xz as provided by lzmaffi by Tomer Chachamu. See also The .xz File Format.
- Zstd as provided by indexed_zstd by Marco Martinelli. See also Zstandard Compression Format.
You can simply install it from PyPI:
pip install ratarmount
Or, if you want to test the latest version:
pip install git+https://github.com/mxmlnkn/ratarmount.git@develop#egginfo=ratarmountYou can also simply download ratarmount.py and call it directly after installing the dependencies manually with: pip3 install --requirement https://raw.githubusercontent.com/mxmlnkn/ratarmount/master/requirements.txt.
In order to use, the xz backend, you currently have to do more manual setup because lzmaffi does not provide wheels. On Ubuntu 20.10 or similar systems, the setup would look like this:
sudo apt install liblzma-dev
pip3 install --user cffi # Necessary because of a bug(?) in the lzmaffi setup.py
pip3 install --user lzmaffiusage: ratarmount [-h] [-f] [-d DEBUG] [-c] [-r] [-gs GZIP_SEEK_POINT_SPACING]
[-p PREFIX] [-e ENCODING] [-i] [--verify-mtime] [-s]
[--index-file INDEX_FILE] [--index-folders INDEX_FOLDERS]
[-o FUSE] [-v]
mount_source [mount_source ...] [mount_point]
With ratarmount, you can:
- Mount a (compressed) TAR file to a folder for read-only access
- Mount a compressed file to `<mountpoint>/<filename>`
- Bind mount a folder to another folder for read-only access
- Union mount a list of TARs, compressed files, and folders to a mount point
for read-only access
positional arguments:
mount_source The path to the TAR archive to be mounted. If multiple
archives and/or folders are specified, then they will
be mounted as if the arguments coming first were
updated with the contents of the archives or folders
specified thereafter, i.e., the list of TARs and
folders will be union mounted.
mount_point The path to a folder to mount the TAR contents into.
If no mount path is specified, the TAR will be mounted
to a folder of the same name but without a file
extension. (default: None)
optional arguments:
-h, --help show this help message and exit
-f, --foreground Keeps the python program in foreground so it can print
debug output when the mounted path is accessed.
(default: False)
-d DEBUG, --debug DEBUG
Sets the debugging level. Higher means more output.
Currently, 3 is the highest. (default: 1)
-c, --recreate-index If specified, pre-existing .index files will be
deleted and newly created. (default: False)
-r, --recursive Mount TAR archives inside the mounted TAR recursively.
Note that this only has an effect when creating an
index. If an index already exists, then this option
will be effectively ignored. Recreate the index if you
want change the recursive mounting policy anyways.
(default: False)
-gs GZIP_SEEK_POINT_SPACING, --gzip-seek-point-spacing GZIP_SEEK_POINT_SPACING
This only is applied when the index is first created
or recreated with the -c option. The spacing given in
MiB specifies the seek point distance in the
uncompressed data. A distance of 16MiB means that
archives smaller than 16MiB in uncompressed size will
not benefit from faster seek times. A seek point takes
roughly 32kiB. So, smaller distances lead to more
responsive seeking but may explode the index size!
(default: 16)
-p PREFIX, --prefix PREFIX
[deprecated] Use "-o modules=subdir,subdir=<prefix>"
instead. This standard way utilizes FUSE itself and
will also work for other FUSE applications. So, it is
preferable even if a bit more verbose.The specified
path to the folder inside the TAR will be mounted to
root. This can be useful when the archive as created
with absolute paths. E.g., for an archive created with
`tar -P cf /var/log/apt/history.log`, -p /var/log/apt/
can be specified so that the mount target directory
>directly< contains history.log. (default: )
-e ENCODING, --encoding ENCODING
Specify an input encoding used for file names among
others in the TAR. This must be used when, e.g.,
trying to open a latin1 encoded TAR on an UTF-8
system. Possible encodings: https://docs.python.org/3/
library/codecs.html#standard-encodings (default:
utf-8)
-i, --ignore-zeros Ignore zeroed blocks in archive. Normally, two
consecutive 512-blocks filled with zeroes mean EOF and
ratarmount stops reading after encountering them. This
option instructs it to read further and is useful when
reading archives created with the -A option. (default:
False)
--verify-mtime By default, only the TAR file size is checked to match
the one in the found existing ratarmount index. If
this option is specified, then also check the
modification timestamp. But beware that the mtime
might change during copying or downloading without the
contents changing. So, this check might cause false
positives. (default: False)
-s, --strip-recursive-tar-extension
If true, then recursively mounted TARs named
<file>.tar will be mounted at <file>/. This might lead
to folders of the same name being overwritten, so use
with care. The index needs to be (re)created to apply
this option! (default: False)
--index-file INDEX_FILE
Specify a path to the .index.sqlite file. Setting this
will disable fallback index folders. (default: None)
--index-folders INDEX_FOLDERS
Specify one or multiple paths for storing
.index.sqlite files. Paths will be tested for
suitability in the given order. An empty path will be
interpreted as the location in which the TAR resides.
If the argument begins with a bracket "[", then it
will be interpreted as a JSON-formatted list. If the
argument contains a comma ",", it will be interpreted
as a comma-separated list of folders. Else, the whole
string will be interpreted as one folder path.
Examples: --index-folders ",~/.foo" will try to save
besides the TAR and if that does not work, in ~/.foo.
--index-folders '["~/.ratarmount", "foo,9000"]' will
never try to save besides the TAR. --index-folder
~/.ratarmount will only test ~/.ratarmount as a
storage location and nothing else. Instead, it will
first try ~/.ratarmount and the folder "foo,9000".
(default: ,~/.ratarmount)
-o FUSE, --fuse FUSE Comma separated FUSE options. See "man mount.fuse" for
help. Example: --fuse
"allow_other,entry_timeout=2.8,gid=0". (default: )
-v, --version Print version string. (default: False)
In order to reduce the mounting time, the created index for random access to files inside the tar will be saved to one of these locations. These locations are checked in order and the first, which works sufficiently, will be used. This is the default location order:
- .index.sqlite
- ~/.ratarmount/<path to tar: '/' -> '_'>.index.sqlite E.g., ~/.ratarmount/_media_cdrom_programm.tar.index.sqlite
This list of fallback folders can be overwritten using the --index-folders
option. Furthermore, an explicitly named index file may be specified using
the --index-file option. If --index-file is used, then the fallback
folders, including the default ones, will be ignored!
The mount sources can be TARs and/or folders. Because of that, ratarmount
can also be used to bind mount folders read-only to another path similar to
bindfs and mount --bind. So, for:
ratarmount folder mountpoint
all files in folder will now be visible in mountpoint.
If multiple mount sources are specified, the sources on the right side will be added to or update existing files from a mount source left of it. For example:
ratarmount folder1 folder2 mountpoint
will make both, the files from folder1 and folder2, visible in mountpoint.
If a file exists in both multiple source, then the file from the rightmost
mount source will be used, which in the above example would be folder2.
If you want to update / overwrite a folder with the contents of a given TAR, you can specify the folder both as a mount source and as the mount point:
ratarmount folder file.tar folder
The FUSE option -o nonempty will be automatically added if such a usage is detected. If you instead want to update a TAR with a folder, you only have to swap the two mount sources:
ratarmount file.tar folder folder
If a file exists multiple times in a TAR or in multiple mount sources, then the hidden versions can be accessed through special .versions folders. For example, consider:
ratarmount folder updated.tar mountpoint
and the file foo exists both in the folder and as two different versions
in updated.tar. Then, you can list all three versions using:
ls -la mountpoint/foo.versions/
dr-xr-xr-x 2 user group 0 Apr 25 21:41 .
dr-x------ 2 user group 10240 Apr 26 15:59 ..
-r-x------ 2 user group 123 Apr 25 21:41 1
-r-x------ 2 user group 256 Apr 25 21:53 2
-r-x------ 2 user group 1024 Apr 25 22:13 3
In this example, the oldest version has only 123 bytes while the newest and by default shown version has 1024 bytes. So, in order to look at the oldest version, you can simply do: cat mountpoint/foo.versions/1
If you want a compressed file not containing a TAR, e.g., foo.bz2, then
you can also use ratarmount for that. The uncompressed view will then be
mounted to <mountpoint>/foo and you will be able to leverage ratarmount's
seeking capabilities when opening that file.
In contrast to bzip2 and gzip compressed files, true seeking on xz and zst files is only possible at block or frame boundaries. This wouldn't be noteworthy, if both standard compressors for xz and zstd were not by default creating unsuited files. Even though both file formats do support multiple frames and xz even contains a frame table at the end for easy seeking, both compressors write only a single frame and/or block out, making this feature unusable. In order to generate truly seekable compressed files, you'll have to use pixz for xz files. For zstd compressed, you can try with t2sz. The standard zstd tool does not support setting smaller block sizes yet although an issue does exist. Alternatively, you can simply split the original file into parts, compress those parts, and then concatenate those parts together to get a suitable multiframe zst file. Here is a bash function, which can be used for that:
createMultiFrameZstd()
(
# Detect being piped into
if [ -t 0 ]; then
file=$1
frameSize=$2
if [[ ! -f "$file" ]]; then echo "Could not find file '$file'." 1>&2; return 1; fi
fileSize=$( stat -c %s -- "$file" )
else
if [ -t 1 ]; then echo 'You should pipe the output to somewhere!' 1>&2; return 1; fi
echo 'Will compress from stdin...' 1>&2
frameSize=$1
fi
if [[ ! $frameSize =~ ^[0-9]+$ ]]; then
echo "Frame size '$frameSize' is not a valid number." 1>&2
return 1
fi
# Create a temporary file. I avoid simply piping to zstd
# because it wouldn't store the uncompressed size.
if [[ -d --tmpdir=/dev/shm ]]; then frameFile=$( mktemp --tmpdir=/dev/shm ); fi
if [[ -z $frameFile ]]; then frameFile=$( mktemp ); fi
if [[ -z $frameFile ]]; then
echo "Could not create a temporary file for the frames." 1>&2
return 1
fi
if [ -t 0 ]; then
true > "$file.zst"
for (( offset = 0; offset < fileSize; offset += frameSize )); do
dd if="$file" of="$frameFile" bs=$(( 1024*1024 )) \
iflag=skip_bytes,count_bytes skip="$offset" count="$frameSize" 2>/dev/null
zstd -c -q -- "$frameFile" >> "$file.zst"
done
else
while true; do
dd of="$frameFile" bs=$(( 1024*1024 )) \
iflag=count_bytes count="$frameSize" 2>/dev/null
# pipe is finished when reading it yields no further data
if [[ ! -s "$frameFile" ]]; then break; fi
zstd -c -q -- "$frameFile"
done
fi
'rm' -f -- "$frameFile"
)In order to compress a file named foo into a multiframe zst file called foo.zst, which contains frames sized 4MiB of uncompressed ata, you would call it like this:
createMultiFrameZstd foo $(( 4*1024*1024 ))It also works when being piped to. This can be useful for recompressing files to avoid having to decompress them first to disk.
lbzip2 -cd well-compressed-file.bz2 | createMultiFrameZstd $(( 4*1024*1024 )) > recompressed.zstYou downloaded a large TAR file from the internet, for example the 1.31TB large ImageNet, and you now want to use it but lack the space, time, or a file system fast enough to extract all the 14.2 million image files.
Archivemount seems to have large performance issues for too many files for both mounting and file access in version 0.8.7. A more in-depth comparison benchmark can be found here.
- Mounting the 6.5GB ImageNet Large-Scale Visual Recognition Challenge 2012 validation data set, and then testing the speed with:
time cat mounted/ILSVRC2012_val_00049975.JPEG | wc -ctakes 250ms for archivemount and 2ms for ratarmount. - Trying to mount the 150GB ILSVRC object localization data set containing 2 million images was given up upon after 2 hours. Ratarmount takes ~15min to create a ~150MB index and <1ms for opening an already created index (SQLite database) and mounting the TAR. In contrast, archivemount will take the same amount of time even for subsequent mounts.
- Does not support recursive mounting. Although, you could write a script to stack archivemount on top of archivemount for all contained TAR files.
Tarindex is a command line to tool written in Python which can create index files and then use the index file to extract single files from the tar fast. However, it also has some caveats which ratarmount tries to solve:
- It only works with single files, meaning it would be necessary to loop over the extract-call. But this would require loading the possibly quite large tar index file into memory each time. For example for ImageNet, the resulting index file is hundreds of MB large. Also, extracting directories will be a hassle.
- It's difficult to integrate tarindexer into other production environments. Ratarmount instead uses FUSE to mount the TAR as a folder readable by any other programs requiring access to the contained data.
- Can't handle TARs recursively. In order to extract files inside a TAR which itself is inside a TAR, the packed TAR first needs to be extracted.
I didn't find out about TAR Browser before I finished the ratarmount script. That's also one of it's cons:
- Hard to find. I don't seem to be the only one who has trouble finding it as it has zero stars on Github after 4 years compared to 29 stars for tarindexer after roughly the same amount of time.
- Hassle to set up. Needs compilation and I gave up when I was instructed to set up a MySQL database for it to use. Confusingly, the setup instructions are not on its Github but here.
- Doesn't seem to support recursive TAR mounting. I didn't test it because of the MysQL dependency but the code does not seem to have logic for recursive mounting.
- Xz compression also is only block or frame based, i.e., only works faster with files created by pixz or pxz.
Pros:
- supports bz2- and xz-compressed TAR archives
Ratarmount creates an index file with file names, ownership, permission flags, and offset information to be stored at the TAR file's location or inside ~/.ratarmount/ and then offers a FUSE mount integration for easy access to the files.
The test with the first version (50e8dbb), which used the removed pickle backend for serializing the metadata index, for the ImageNet data set is promising:
- TAR size: 1.31TB
- Contains TARs: yes
- Files in TAR: ~26 000
- Files in TAR (including recursively in contained TARs): 14.2 million
- Index creation (first mounting): 4 hours
- Index size: 1GB
- Index loading (subsequent mounting): 80s
- Reading a 40kB file: 100ms (first time) and 4ms (subsequent times)
The reading time for a small file simply verifies the random access by using file seek to be working. The difference between the first read and subsequent reads is not because of ratarmount but because of operating system and file system caches.
Here is a more recent test for version 0.2.0 with the new default SQLite backend:
- TAR size: 124GB
- Contains TARs: yes
- Files in TAR: 1000
- Files in TAR (including recursively in contained TARs): 1.26 million
- Index creation (first mounting): 15m 39s
- Index size: 146MB
- Index loading (subsequent mounting): 0.000s
- Reading a 64kB file: ~4ms
- Running 'find mountPoint -type f | wc -l' (1.26M stat calls): 1m 50s
During the making of this project several benchmarks were created. These can be viewed here. These are some of the things benchmarked and compared there:
- Memory and runtime comparisons of backends for saving the index with offsets
- Comparison of SQLite table designs
- Mounting and file access time comparison between archivemount and ratarmount
If ratarmount helped you out and satisfied you so much that you can't help but want to donate, you can toss a coin to your programmer through one of these addresses:
| Type | Address |
|---|---|
| BTC | bc1qkc7stljxazpkk5lzcj4gqu2tvh0dh4exz4563t |
| ETH | 0xb049e3aC04f08c85A1A12e0e199adECb045C76C8 |
| LTC | LTRbWdUY576MNkhXhXEXNpt3NuY2ecR9F9 |
| XMR | 44DcWgDNxvUJav5zKHprJLJyKx11RyMgEfv3yuuqeUGGec26jRqA9UnaKc2uoKf5TyCVx3CmfZhyQiXtZP1kbdYCRCXNyJS |