On Fri, 27 Apr 2007, Bill Huey wrote:
On Fri, Apr 27, 2007 at 12:50:34PM -0700, Linus Torvalds wrote:
Oh, well.. Journalling sucks.
I was actually _really_ hoping that somebody would come along and tell
everybody that this whole journal-logging is stupid, and that it's just
better to not ever re-write blocks on disk, but instead write to new
blocks with version numbers (and not re-use old blocks until new versions
are stable on disk).
There was even somebody who did something like that for a PhD thesis, I
forget the details (and it apparently died when the thesis was presumably
accepted ;).
That sounds a whole lot like NetApp's WAFL file system and is heavily
patented.
bill
Hi
SpadFS doesn't write to unallocated parts like log filesystems (LFS) or
phase tree filesystems (TUX2); it writes inside normal used structures,
but it marks each structure with generation tags --- when it updates
global table of tags, it atomically makes several structures valid. I
don't know about this idea being used elsewhere.
It's fsync is slow too (needs to write all (meta)data too), but it at
least doesn't livelock --- fsync is basically:
* write all buffers and wait for completion
* take lock preventing metadata updates
* write all buffers again (those that were updated while previous write
was in progress) and wait for completion
* update global generation count table
* release the lock
Maybe Suse will be paying me from this autumn to make more features to it
--- so far it works, doesn't eat data, but isn't much known :)
Mikulas
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