SQUASHFS 3.1 - A squashed read-only filesystem for Linux Copyright 2002-2006 Phillip Lougher Released under the GPL licence (version 2 or later). Welcome to Squashfs version 3.1-r2. Squashfs 3.1 has major improvements to the Squashfs tools (Mksquashfs and Unsquashfs), some major bug fixes, new kernel patches, and various other smaller improvements and bug fixes. Please see the CHANGES file for a detailed list. 1. MKSQUASHFS ------------- Mksquashfs has been rewritten and it is now multi-threaded. It offers the following improvements: 1. Parallel compression. By default as many compression and fragment compression threads are created as there are available processors. This significantly speeds up performance on SMP systems. 2. File input and filesystem output is peformed in parallel on separate threads to maximise I/O performance. Even on single processor systems this speeds up performance by at least 10%. 3. Appending has been significantly improved, and files within the filesystem being appended to are no longer scanned and checksummed. This significantly improves append time for large filesystems. 4. File duplicate checking has been optimised, and split into two separate phases. Only files which are considered possible duplicates after the first phase are checksummed and cached in memory. 5. The use of swap memory was found to significantly impact performance. The amount of memory used to cache the file is now a command line option, by default this is 512 Mbytes. 1.1 NEW COMMAND LINE OPTIONS ---------------------------- The new Mksquashfs program has a couple of extra command line options which can be used to control the new features: -processors This specifies the number of processors used by Mksquashfs. By default this is the number of available processors. -read_queue This specifies the size of the file input queue used by the reader thread. This defaults to 64 Mbytes. -write_queue This specifies the size of the filesystem output queue used by the writer thread. It also specifies the maximum cache used in file duplicate detection (the output queue is shared between these tasks). This defaults to 512 Mbytes. 1.2 PERFORMANCE RESULTS ----------------------- The following results give an indication of the speed improvements. Two example filesystems were tested, a liveCD filesystem (about 1.8 Gbytes uncompressed), and my home directory consisting largely of text files (about 1.3 Gbytes uncompressed). Tests were run on a single core and a dual core system. Dual Core (AMDx2 3800+) system: Source directories on ext3. LiveCD, old mksquashfs: real 11m48.401s user 9m27.056s sys 0m15.281s LiveCD, new par_mksquashfs: real 4m8.736s user 7m11.771s sys 0m27.749s "Home", old mksquashfs: real 4m34.360s user 3m54.007s sys 0m32.155s "Home", new par_mksquashfs: real 1m27.381s user 2m7.304s sys 0m17.234s Single Core PowerBook (PowerPC G4 1.5 GHz Ubuntu Linux) Source directories on ext3. LiveCD, old mksquashs: real 11m38.472s user 9m6.137s sys 0m23.799s LiveCD, par_mksquashfs: real 10m5.572s user 8m59.921s sys 0m16.145s "Home", old mksquashfs: real 3m42.298s user 2m49.478s sys 0m13.675s "Home", new par_mksquashfs: real 3m9.178s user 2m50.699s sys 0m9.069s I'll be interested in any performance results obtained, especially from SMP machines larger than my dual-core AMD box, as this will give an indication of the scalability of the code. Obviously, I'm also interested in any problems, deadlocks, low performance etc. 2. UNSQUASHFS ------------- Unsquashfs now allows you to specify the filename or directory that is to be extracted from the Squashfs filesystem, rather than always extracting the entire filesystem. It also has a new "-force" option, and all options can be specified in a short form (-i rather than -info). The Unsquashfs usage info is now: SYNTAX: ./unsquashfs [options] filesystem [directory or file to extract] -v[ersion] print version, licence and copyright information -i[nfo] print files as they are unsquashed -l[s] list filesystem only -d[est] unsquash to , default "squashfs-root" -f[orce] if file already exists then overwrite To extract a subset of the filesystem, the filename or directory tree that is to be extracted can now be specified on the command line. The file/directory should be specified using the full path to the file/directory as it appears within the Squashfs filesystem. The file/directory will also be extracted to that position within the specified destination directory. The new "-force" option forces Unsquashfs to output to the destination directory even if files or directories already exist. This allows you to update an existing directory tree, or to Unsquashfs to a partially filled directory. Without the "-force" option, Unsquashfs will refuse to overwrite any existing files, or to create any directories if they already exist. This is done to protect data in case of mistakes, and so the "-force" option should be used with caution.