Re: shadowfs
On Sat, May 13, 2000 at 10:24:22PM +0200, Norbert Nemec wrote:
> OK, that would basically be a way for read-only shadowfs. If that's all we
> aim at, there should not be a problem for the specifications. Just layer the
> whole tree (ignoring contents of non-readable directories) If a file exists
> in more than one versions, choose the "topmost" one. Everything beyond that
> (like filename patterns etc.) would be additional features that do not
> change the basic concept.
>
> Question is, whether read-only is the only thing we want to go for. It would
> be absolutly neat, if we had a way to layer filesystems in a absolutely
> transparent way, so one could do things like have a read-only system as base
> (maybe NFS-shared by several computers?) and a read-write system on top that
> takes any changes you make and perhaps copies of frequently used files for
> better performance.
When we'll have r/o shadow, it won't be very hard to make it simple r/w.
At first, there could be 1 r/w + 1 or more r/o subfs.
This is easy for modifying files from r/w fs and creating new files.
You only have to create subdirs that exists on one of r/o's and not yet on r/w,
and forward all calls to r/w fs.
More problems arise with modifying files that exist only on r/o, deleting files,
renaming, etc.
> Imagine a pre-installed system distributed on DVD (several GB in size) that
> you can use just as any normal system, since it writes only the changes on a
> fairly small partition (or even a ramdisk)
Problems with ramdisk is that some stuff /etc/* /var/mail/* should be available
between reboots, so such system would need NFS or smal hd/zip/... to do anything
useful.
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