Robert Milkowski wrote: > Hello zfs-discuss, > > http://git.kernel.org/?p=linux/kernel/git/mason/btrfs-unstable-standalone.git;a=commit;h=eecfe5255c533fefd38072a04e4afb56c40d9719 > "If compression for a given set of pages fails to make them smaller, the > file is flagged to avoid future compression attempts later." > > Maybe that's a good one - so if couple of blocks do not compress then > flag it in file metadata and do not try to compress any blocks within > the file anymore. Of course for some files it will be suboptimal so > maybe a dataset option?
I don't understand why having a couple of blocks in a file not compressible should cause the whole file not to be - that to me seems like a bad idea. What if for example the file is a disk image and the first couple of blocks aren't compressible but huge chunks of it are ? ZFS does compression at the block level and attempts it on every write. If a given block doesn't compress sufficiently well (hardcoded 12.5%) or at all then the block is tagged as ZIO_COMPRESS_OFF in the blkptr. That doesn't impact any other blocks though. So what would the dataset option you mention actually do ? What problem do you think needs solved here ? -- Darren J Moffat _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
