I am trying to use Btrfs' compression on some highly compressible data. I try to make zstd give better performance than 34:1.
This: $ truncate -s 1T /tmp/btrfs $ mkfs.btrfs /tmp/btrfs $ mount -o compress=zstd:9 /tmp/btrfs /mnt/btrfs $ head -c 10G /dev/zero > /mnt/btrfs/zero $ du /tmp/btrfs 313672k shows a compression ratio of 10737418240/312724/1024 = 33.5:1 But if I run: $ head -c 10G /dev/zero | zstd | wc -c 336655 I get a compression ratio of 10737418240/336655 = 31894:1 That is around 1000 times better. I understand there is some overhead in Btrfs, so it is expected that it is not possible to reach the full ratio. But it seems there is little to no difference in using 'compress=zstd:9' and 'compress=zstd:3' on highly compressible data. My guess is, that data is chopped up in small blocks (1k?) that are each compressed. If so: Is it possible to make these blocks bigger? I think that would make sense in general when using higher compression values. /Ole
