Bob Friesenhahn wrote: > On Wed, 5 Nov 2008, David Gwynne wrote: > > >> be done in a very short time. perhaps you can amortize that cost by >> doing it when the data from userland makes it into the kernel. another >> idea could be doing the compression when you reach a relatively low >> threshold of uncompressed data in the cache. ie, as soon as you get >> 1MB of data in the cache, compress it then, rather than waiting till >> you have 200MB of data in the cache that needs to be compressed RIGHT >> NOW. >> > > This is counter-productive. ZFS's lazy compression approach ends up > doing a lot less compression in the common case where files are > updated multiple times before ZFS decides to write to disk. If your > advice is followed, then every write will involve compression, rather > than the summation of perhaps thousands of writes. > > But gzip has a significant impact when doing a zfs receive. It would be interesting to see how an amortised compression scheme would work in this case. Currently writing to a filesystem with gzip compression takes more than twice the time than a to one with lzjb compression on a quiet x4540. There isn't any noticeable difference between lzjb and no compression.
-- Ian. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
