Re: Spare disk could not sleep / standby

On Tuesday March 8, molle.bestefich@gmail.com wrote:

Neil Brown wrote:

quoted

Then after 20ms with no write, they are all marked 'clean'.
Then before the next write they are all marked 'active'.

As the event count needs to be updated every time the superblock is
modified, the event count will be updated forever active->clean or
clean->active transition.

So..  Sorry if I'm a bit slow here.. But what you're saying is:

The kernel marks the partition clean when all writes have expired to disk.
This change is propagated through MD, and when it is, it causes the
event counter to rise, thus causing a write, thus marking the
superblock active.  20 msecs later, the same scenario repeats itself.

Is my perception of the situation correct?

No.  Writing the superblock does not cause the array to be marked
active.
If the array is idle, the individual drives will be idle.

Seems like a design flaw to me, but then again, I'm biased towards
hating this behaviour since I really like being able to put inactive
RAIDs to sleep..

Hmmm... maybe I misunderstood your problem.  I thought you were just
talking about a spare not being idle when you thought it should be.
Are you saying that your whole array is idle, but still seeing writes?
That would have to be something non-md-specific I think.

NeilBrown

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Neil Brown wrote:

quoted

Is my perception of the situation correct?

No.  Writing the superblock does not cause the array to be marked
active.
If the array is idle, the individual drives will be idle.

Ok, thank you for the clarification.

quoted

Seems like a design flaw to me, but then again, I'm biased towards
hating this behaviour since I really like being able to put inactive
RAIDs to sleep..

Hmmm... maybe I misunderstood your problem.  I thought you were just
talking about a spare not being idle when you thought it should be.
Are you saying that your whole array is idle, but still seeing writes?
That would have to be something non-md-specific I think.

No, the confusion is my bad.
That was the original problem posted by Peter Evertz, which you
provided a workaround for.

_I_ was just curious about the workings of MD in 2.6, since it sounded
a bit like it wasn't possible to put a RAID array to sleep.  I'm about
to upgrade a server to 2.6, which "needs" to spin down when idle.  Got
a bit worried for a moment there =).

Thanks again.