Messages in this thread | | | Date | Wed, 5 Jul 2006 17:36:39 -0700 | From | Valerie Henson <> | Subject | Blatant layering violations (was Re: ext4 features) |
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On Mon, Jul 03, 2006 at 10:55:23PM +0200, Tomasz Torcz wrote: > > ZFS was already called ,,blatant layering violation''. ;)
I kind of like the phrase "blatant layering violation" - catchy, isn't it? The main reason people think of ZFS as a blatant layering violation is because it has the letters "FS" in the name, but it does a lot more than a file system. ZFS actually includes three distinct layers with well-defined interfaces, none of which directly maps to most people's conception of a "file system."
The really painfully short summary of the layers is:
SPA - Storage Pool Allocator, disks go into the bottom, virtually addressed, explicitly freed/allocated blocks come out of the top
DMU - Data Management Unit, virtually addressed blocks go in the bottom, plain objects come out the top (an object is like a file with no dangly bits like permissions, etc.)
ZPL - ZFS POSIX Layer, plain objects go in the bottom, VFS ops come out the top
For a really nice, much more detailed ZFS source tour, see:
http://www.opensolaris.org/os/community/zfs/source/
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