ZFS feature flags

[Paul Ciarlo]

It seems the ZFS-on-Linux team has taken the initiative and added a few
pool features, that, when enabled, break write support on the other
implementation of ZFS that I'm aware of, and, are enabled by default upon
pool creation or upgrade unless explicitly disabled or the -n flag is
specified.

Unfortunately they are enabled on the pool created by the ZFS graphical
installer, which renders the pool read-only on most other implementations
on most other operating systems, and even just old versions of ZoL.

So, I am just wondering if there's any support for the opinion that any
pool features not universally or nearly universally be turned off by
default, and frankly most of these are either unintelligible or practically
useless even in the very specific use cases they were apparently (badly)
designed for, so we won't be missing out on much. Consulting the chart we
can see the worst offenders are 0.8 features like bookmarks_v2,
project_quota, allocation_classes, resilver_defer.

http://open-zfs.org/wiki/Feature_Flags

Yeah just look at this mess. Replacing ordered pool versioning numbers with
an unordered set of random strings didn't turn out to be a very good idea
IMO, and now we have to consult something like this considering all the ZFS
implementations we're currently using and may or may not be using in the
indefinite future. Of course sure you can backup the pool and create a new
one without the flags, I just did in fact, but it seems like an unnecessary
evil wrought by the chaos that is ZFS development in lieu of any open
sourcing or leadership by Oracle that we can easily avoid.

Paul

<http://open-zfs.org/wiki/Feature_Flags>
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