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Btrfs LZO Compression Performance

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  • #16
    Originally posted by mbouchar View Post
    It's not complicated. These tests only shows that the stuff is compressed sometimes in memory before being written to disk. This is the same thing that happens when encrypted disks shows better performance than normal disks.

    Only that your memory and CPU will be taxed more and you will have a slower computer for other stuff.
    it's a pretty well established idea that on-disk compression can (and does) lead to impressive performance increase under many workloads. it's not a simple "yay" or "nay". the fact is in the time your disk seeks once your CPU has already burned thru several million cycles ... it's like light speed vs. the fastest human vehicle -- anything you can shave off the latter is probably a win, even if it already seems "pretty fast".

    there are even several workloads that benefit from _memory_ compression ... because RAM -- the uber spaceship of 2010+ -- is still peanuts compared to C. everything that isn't your CPU is a cache to your CPU; the less time to get it there the better. data locality is king.

    http://lwn.net/Articles/426853/

    "Zcache doubles RAM efficiency while providing a significant performance boost on many workloads."

    both zcache and btrfs (not sure ZFS) use LZO ... the simple truth is your CPU is a lazy bastard that spends most of it's time blaming it's poor efficiency on the rest of the team ;-)

    C Anthony

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    • #17
      I use btrfs + lzo compression on the latest linux images for the O2 Joggler.

      http://joggler.exotica.org.uk/
      http://en.wikipedia.org/wiki/O2_Joggler

      using slow usb flash devices (mine is ~9mb write and ~27mb/second read),. btrfs with lzo feels significantly faster than using zlib (and less cpu usage). Not an actual benchmark of course

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      • #18
        Me too, I think this testing should run on some video file to see the real benefit of compression.

        I don;t think 9X iozone testing result can apply to real world.

        Originally posted by BenderRodriguez View Post
        Why do i get the feeling that zlib/lzo mode speeds up iozone and fs-mark only because the created files are empty and thus compress almost infintely good ?

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        • #19
          Originally posted by mbouchar View Post
          It's not complicated. These tests only shows that the stuff is compressed sometimes in memory before being written to disk. This is the same thing that happens when encrypted disks shows better performance than normal disks.

          Only that your memory and CPU will be taxed more and you will have a slower computer for other stuff.
          only that ram is dirt cheap and cpu's underworked almost all the time.

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          • #20
            It only needs fsck now!

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            • #21
              Originally posted by crazycheese View Post
              It only needs fsck now!
              Understatement of the year by far!

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