Re: [RFC 0/13] extents and 48bit ext3

Andrew Morton wrote:
Ted&co have been pretty good at avoiding compatibility problems.

Well, extents and 48bit make that track record demonstrably worse.

Users are now forced to remember that, if they write to their filesystem after using either $mmver or $korgver kernels, they are locked out of using older kernels.

From the user's perspective, ext3 has no clear "metadata version 1", "metadata version 2" division. Thus they are now forced to keep a matrix of kernel versions and ext3 feature flag support, to know which kernels are usable with which data. It is a support nightmare.

At no point is a user ever told, in big capital letters, "IF YOU WRITE TO THIS FILESYSTEM, YOU CAN'T BOOT OLDER KERNELS." There is no "click OK to continue with this dramatic event."

And as features continue to be added in this manner, this problem gets _exponentially_ worse.


On the project management side of things, I see no indication that this momentum slow -- which implies to me that people will keep slapping new stuff into ext3, rather than directing energy towards a newer, cleaner ext-NG filesystem.

Dragging around back-compat really constrains freedom, and you have to have some sort of "pressure relief valve" (a massive, wildly incompatible update) eventually.

In my mind, it's analagous to locking developers into developing and deploying new features into a stable branch of software. The hacks just get worse and worse, as you bend over backwards for back-compat.

Jeff


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