Re: 3.0 wishlist Was: Overview of 2.2.x goals?

Viet-Trung Luu (vluu@calum.csclub.uwaterloo.ca)
Thu, 22 Jan 1998 00:51:57 -0500 (EST)

Stefan Monnier wrote:
> Brad Keryan <keryan@andrew.cmu.edu> writes:
> > Log-structured filesystems sound extremely good on paper. Is there a
> > stable, fast, log-structured filesystem for any OS at this point?
>
> AIX's LFS, IRIX's XFS, Digital Unix's AdvFS. These are pretty fast and stable.
> WinNT's NTFS is supposed to be log-structured too and reasonably stable (don't
> know about speed, but making anything fast within WinNT is not easy).
>
> SunOS's ufs has also been hacked by adding a log to it. I don't know if it's
> fast and/or stable, though.
>
> Of course, there's also BSD's LFS, but I don't know if it's stable in any
> current BSD derivative.

Doesn't AIX use "JFS"? In any case, JFS, XFS, AdvFS, and NTFS are
"journalling" (they log meta-data changes, and possibly other things,
but that's *separate* from the main structure of the FS), not
log-structured.

BSD's LFS is log-structured -- everything is appended to a log, so
blocks and inodes move around... *all* writes are done at the "end"
("tail"?) of the log.

In any case, log-structured FSes pay a large performance penalty
whenever they have to go and actually do a read off disk (for most
systems, it's probably an overall win, but for some, it could be a big
loss).

I don't know of any other log-structured FS, though. Network Appliance's
WAFL (used on their FAServers) is incredibly cool (but probably
complicated). See http://www.netapp.com/technology/level3/3002.html.

- Trung