[BBLISA] filesystems supporting snapshots

[Dean Anderson]

On Wed, 22 Aug 2007, Tom Metro wrote:

> I've also wondered, given the value of that feature, why we haven't seen 
> it appear in one of the community developed, open source file systems.

AFS has always supported a single snapshot. There is current work 
underway to support multiple snapshots in AFS.  But of course, you 
probably want a local filesystem with full unix semantics. DFS has full 
unix semantics, but still isn't local.  

The BSD log structured fs stuff never got the hoped-for performance.  
Don't confuse the goals with the results.  

Great summary on ZFS and CDDL!  ZFS looks like the best thing going on
the bullet points, but is still encumbered. So if you are thinking
about developing a GPL filesystem, don't even look at this. I'd suggest
that you look at AFS & DFS code and how they do snapshots, and then
graft something like that into Ext3, maybe. Or just start from scratch.

		--Dean

> 
> Jeff Wasilko wrote:
> > ZFS from Sun gets you pretty much everything that Netapp has
> > (filesystem-wise), and more.
> 
> I guess Sun saved the community the trouble of developing it (and 
> conveniently patented all the best parts).
> 
> Sun opens ZFS source code
> http://arstechnica.com/news.ars/post/20051117-5595.html
> 
> This 2005 article gives some background on ZFS and says:
> 
>    So, now that the ZFS source code is available for use, will we be
>    seeing it in Linux sometime soon? According to a Sun FAQ about ZFS, a
>    Linux port "is currently being investigated."
> 
> 
> And then an article from about a year ago:
> http://www.linuxinsight.com/zfs_filesystem_for_linux.html
> 
>    When ZFS was first announced, I'm sure many Linux hackers had a
>    thought how it would be a great idea to port such a great filesystem
>    to Linux. Unfortunately, ZFS source is distributed under Sun's CDDL
>    license which is (some say deliberately) incompatible with the GPL
>    license that Linux kernel uses. So, it looks like there will be no
>    native port of ZFS for Linux in the foreseeable future. What a pity.
> 
> (More in the license issues here:
> http://zfs-on-fuse.blogspot.com/2007/04/zfs-in-linux-kernel.html )
> 
>    Still, lurking around the web, I have found the next best thing, a
>    project to port ZFS to the popular FUSE framework: ZFS on
>    FUSE/Linux[1].
> 
>    Thanks to relieved FUSE licensing, which allows dynamically linking
>    with it without any restrictions, it looks like it's possible to port
>    ZFS to FUSE without any licensing problems. Of course, implementation
>    of filesystem in userspace can never reach speed and stability of
>    in-kernel filesystems, but I still find it very interesting.
> 
> 1. http://www.wizy.org/wiki/ZFS_on_FUSE
> and http://zfs-on-fuse.blogspot.com/
> 
> So it is already available on Linux, but in toy form. So much for 
> creating a low-cost NAS using ZFS. I guess there is always FreeBSD[2].
> 
> 2. http://lists.freebsd.org/pipermail/freebsd-current/2007-April/070544.html
> 
>   -Tom
> 
> 

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