Re: New feature Idea

[jim owens <jowens@hp.com>]

Joe Peterson wrote:
> My thoughts on what you are saying is that it is not generally a good
> idea to assume any filesystem will lay things out in any specific way,
> including whether it has one-to-one mapping of files to blocks.  In
> other words, making a copy of a file on the same filesystem for safety
> reasons (unless you are modifying a file and want a backup of its old
> state, like emacs' ~ files) is probably not a great habit to get into.
> 
> The implementation details of how a filesystem makes things safer should
> be behind-the-scenes (like checksums, multiple-copies-by-default,
> mirroring, etc.).  That way, you can simply rely on the filesystem to
> manage protection of your data rather than going to the effort of
> managing multiple copies of files yourself for that reason.

I'm a filesystem guy so I only use ones I know do what I want,
I never trust ones I don't know about :)

I agree with you about the danger of assuming what a filesystem
will or won't do on local copies.  I also fear that 99% of normal
users have an expectation that making a copy makes a new physical
instance (which of course is not safe if the device crashes either).

I hate dealing with customers that have lost their data because
of the filesystem.


Morey Roof wrote:
> I was hoping to have it specified as a set of mount options or defaults 
> controlled in the super block so that if you want to use it you can 
> otherwise it doesn't exist.

I don't have veto power in btrfs so my aversion means nothing.

As you say, there are a number of good ways to control it.

If you pursue this, I might suggest having a dedup limit
so they can say "keep at least 2 copies" or "just one".

jim