Re: mdadm: Patch to restrict --size when shrinking unless forced

["John Stoffel" <john@stoffel.org>]

>>>>> "Phil" == Phil Turmel <philip@turmel.org> writes:

Phil> On 10/09/2017 12:10 AM, NeilBrown wrote:
>> If there is some action that mdadm can currently be told to perform, and
>> when it tries to perform that action it corrupts the array, then
>> it is certainly appropriate to teach mdadm not to perform that action.
>> It shouldn't even perform that action with --force.   I agree that
>> changing mdadm like this is complementary to changing the kernel.  Both
>> are useful.

Phil> A certain amount of the trouble with all of this is the english meaning
Phil> of "grow" doesn't really match what mdadm allows.

Phil> Might it be reasonable to reject "--grow" operations that reduce the
Phil> final array size, and introduce the complementary "--reduce" operation
Phil> that rejects array size increases?

I like this idea!  And it wouldn't be hard to implement in mdadm.  

Phil> Both operations would share the current code, just apply a different
Phil> sanity check before proceeding.

Phil> mdadm would then at least not violate the rule of least surprise.