Monday, August 28, 2017

Solaris 10 - fiocompress (UFS file compression) settings

Bernd Schemmer has an interesting post about using fiocompress for file-system level compression of individual files on UFS file systems...

I did some experimentation and found a few more things:

  • Increasing the blocksize from the default of 8192 increases the compression ratio
  • The compression ratio seems to be somewhere between gzip and compress (on a text file)
  • Setting the blocksize to 65536 (64KiB) results in an unreadable and undeletable file (at least with normal tools on test system. This is fixed in the latest recommended patch bundle)
  • Using blocksizes below 8192 also results in unusable files. (I only tested multiples of 2)(This is fixed in the latest recommended patch bundle)
  • fiocompress uses an ioctl call to mark a file as compressed if -m is passed. No method to unmark a marked file exists, even in the filesystem driver. (It is possible to modify the OpenSolaris fiocompress to add an option to just mark (a previously compressed) file as compressed) (Look at ufs_vnops.c for the _FIO_COMPRESSED ioctl implementation)

Test compression code:
ls -lah testfile.txt; du testfile.txt; du -h testfile.txt; for b in 256 512 1024 2048 4096 8192 16384 32768 65536; do fiocompress -b $b -c -m testfile.txt testfile.txt$b; done

Results: (including other common formats)
$ls -lah testfile.txt*
testfile.txt1024: Operation not applicable
testfile.txt2048: Operation not applicable
testfile.txt256: Operation not applicable
testfile.txt4096: Operation not applicable
testfile.txt512: Operation not applicable
testfile.txt65536: Operation not applicable
-rw-r--r--   1 user   group      101M Mar 11 10:26 testfile.txt
-rw-------   1 user   group      4.4M Mar 11 10:29 testfile.txt.7z
-rw-r--r--   1 user   group      5.2M Mar 11 10:26 testfile.txt.bz2
-rw-r--r--   1 user   group      7.2M Mar 11 10:28 testfile.txt.gzip
-rw-r--r--   1 user   group      8.9M Mar 11 10:28 testfile.txt.gzip-1
-rw-r--r--   1 user   group      6.7M Mar 11 10:28 testfile.txt.gzip-9
-rw-r--r--   1 user   group       13M Mar 11 10:27 testfile.txt.Z
-rw-r--r--   1 user   group      7.2M Mar 11 10:32
-rw-r--r--   1 user   group      101M Mar 11 10:55 testfile.txt16384
-rw-r--r--   1 user   group      101M Mar 11 10:55 testfile.txt32768
-rw-r--r--   1 user   group      101M Mar 11 10:55 testfile.txt8192

$du testfile.txt*
206544  testfile.txt
9040    testfile.txt.7z
10624   testfile.txt.bz2
14848   testfile.txt.gzip
18240   testfile.txt.gzip-1
13840   testfile.txt.gzip-9
27632   testfile.txt.Z
18784   testfile.txt16384
16480   testfile.txt32768
22656   testfile.txt8192
$du -h testfile.txt*
 101M   testfile.txt
 4.4M   testfile.txt.7z
 5.2M   testfile.txt.bz2
 7.2M   testfile.txt.gzip
 8.9M   testfile.txt.gzip-1
 6.8M   testfile.txt.gzip-9
  13M   testfile.txt.Z
 9.2M   testfile.txt16384
 8.0M   testfile.txt32768
  11M   testfile.txt8192

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