I was considering looking into installing Void with ZFS on root if I ever need to reinstall the OS on my computer. So far the advantages I have read about have been mostly about snapshotting and restoration but I am admittedly more interested because it’s a shiny new file system.

I am using a laptop with 250GB SSD. Would I benefit from using ZFS? Or is it overhyped? Any input is appreciated.

  • @ksynwaOP
    2•4 years ago

    transparent compression

    I am guessing this means the files are compressed when they are stored on disk. Is the space saved this way significant? I have only 250GB space so it would be nice if it was.

    • @jetlego
      2•4 years ago

      On my system with a ~60GB partition, here is the output of compsize run on my btrfs subvolumes:

      sudo compsize -x /
Processed 299821 files, 195147 regular extents (197447 refs), 159626 inline.
Type       Perc     Disk Usage   Uncompressed Referenced  
TOTAL       40%      5.1G          12G          12G       
none       100%      1.1G         1.1G         1.1G       
zstd        34%      3.9G          11G          11G

      sudo compsize -x /var
Processed 21378 files, 17517 regular extents (17628 refs), 13617 inline.
Type       Perc     Disk Usage   Uncompressed Referenced  
TOTAL       76%      1.5G         1.9G         1.9G       
none       100%      1.1G         1.1G         1.1G       
zstd        39%      317M         800M         787M 

      sudo compsize -x /tmp
Processed 7 files, 5 regular extents (5 refs), 2 inline.
Type       Perc     Disk Usage   Uncompressed Referenced  
TOTAL       99%       48K          48K          48K       
none       100%       48K          48K          48K       
zstd        69%      392B         564B         564B

      sudo compsize -x /home
Processed 50736 files, 184400 regular extents (196958 refs), 19503 inline.
Type       Perc     Disk Usage   Uncompressed Referenced  
TOTAL       78%      9.0G          11G          10G       
none       100%      7.1G         7.1G         6.0G       
zstd        42%      1.8G         4.3G         4.3G

      Which is a savings of 9.3G or 38%. My fstab has the option compress-force=zstd:9 to enable this.

      https://btrfs.wiki.kernel.org/index.php/Compression

      • @ksynwaOP
        2•4 years ago

        That is actually super good. I will have to look into the CPU overhead for compression/decompression.

        Thanks for the detailed answer.

        • @jetlego
          2•4 years ago

          Here’s some extremely unscientific data I collected:

          CPU: Ryzen 2600x with PBO limits maxed
zstd:1 - 38% compression ratio, ~1000MB/s write speed, all cores maxed out
zstd:3 - 35% compression ratio, ~800MB/s write speed, all cores maxed out
zstd:9 - 33% compression ratio, ~217MB/s write speed, all cores between 50% - 100% while running

CPU: Ryzen 2600x cTDP set to 35 watts and only 2 cores & 4 threads enabled to simulate a weak processor
zstd:1 - 400MB/s
zstd:3 - 300MB/s
zstd:9 - 82MB/s

Same compression ratios and CPU usage

          Notes:

          • A NVME SSD with a sequential write speed of >1000MB/s was used.
          • The command used for testing was “pv enwik9 enwik9 enwik9 enwik9 enwik9 enwik9> enwik9.6” where enwik9 is the file from http://prize.hutter1.net/
          • The BTRFS filesystem was on a LUKS encrypted device so there was some AES overhead, but the 2600x supports hardware accelerated AES instructions so it shouldn’t play that large of a role
          • vm.dirty.ratio set to 1
          • Cores enabled were 1 on each CCX
          • Decompression was too fast and was bottlenecked by the SSD
          • @ksynwaOP
            2•4 years ago

            This is some great work. Thank you very much.