> Even the most expensive decompression algorithms > generally run > significantly faster than I/O to disk -- at least > when real disks are > involved. So, as long as you don't run out of CPU > and have to wait for > CPU to be available for decompression, the > decompression will win. The > same concept is true for dedup, although I don't > necessarily think of > dedup as a form of compression (others might > reasonably do so though.)
Effectively, dedup is a form of compression of the filesystem rather than any single file, but one oriented to not interfering with access to any of what may be sharing blocks. I would imagine that if it's read-mostly, it's a win, but otherwise it costs more than it saves. Even more conventional compression tends to be more resource intensive than decompression... What I'm wondering is when dedup is a better value than compression. Most obviously, when there are a lot of identical blocks across different files; but I'm not sure how often that happens, aside from maybe blocks of zeros (which may well be sparse anyway). -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
