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Am 27.02.14 23:27, schrieb Daniel Jozsef:
> Hey ppl ;) I've been wondering about "version 5000", and what it
> signifies. Does this bump mean a fork from Oracle's code? Will
> there be a 5001, 5002, 5099, etc. in the future, on a path separate
> and incompatible from Oracle's versions? Or is it just some kind of
> nonsense number, like setting Samba OS level to MAXINT? :) Is v5000
> identical to v28 or does it indicate some kind of incremental
> update to 28?
the pool version 5000 indicates pools that support the so-called
feature flags.
A version 5000 pool with no specific features turned on is essentially
a v28 pool with the same on-disk data layout.
Feature flags are a way to solve the problem of potentially
incompatible changes to the on-disk data structures in the absence of
a central authority that defines what a given version of the software
should support.
Instead of incrementing the pool version by one every time an
incompatible change occurred and coordinating the version increase
across all independent implementations of ZFS, now any implementation
can define new features that are supported by that implementation and
possibly some other implementations that pickup the change.
Such a pool can be imported read-only by any implementation that
support reading all features active in the pool and read-write by any
implementation that support writing all active features. Some
features are defined as only requiring implementation support for
writing, that is a pool with such a feature active can be imported
read-only by an implementation that has no support for the feature.
Since feature are technically pool properties, there is no reason to
ever again increase the pool version to support new features. As
such, the "5000" in pool version 5000 is just an arbitrary number made
up to distinguish feature flag enabled pools from legacy Oracle pools.
Hope that clarifies it a bit.
Björn
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