> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Brandon High > > Dedup is to > save space, not accelerate i/o.
I'm going to have to disagree with you there. Dedup is a type of compression. Compression can be used for storage savings, and/or acceleration. Fast and lightweight compression algorithms (lzop, v.42bis, v.44) are usually used in-line for acceleration, while a compute-expensive algorithms (bzip2, lzma, gzip) are usually used for space savings and rarely for acceleration (except when transmitting data across a slow channel). Most general-purpose lossless compression algorithms (and certainly most of the ones I just mentioned) achieve compression by reducing duplicated data. There are special purpose lossless (flac etc) and lossy (jpg, mp3 etc) which do other techniques. But general purpose compression might possibly even be exclusively algorithms for reduction of repeated data. Unless I'm somehow mistaken, the performance benefit of dedup comes from the fact that it increases cache hits. Instead of having to read a thousand duplicate blocks from different sectors of disks, you read it once, and the other 999 have all been stored "same as" the original block, so it's 999 cache hits and unnecessary to read disk again. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
