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