Re: [PATCH 1/1] : Spinning up disk is observed on standby paths until timeout, resulting in longer path restoration time.

[Matthew Wilcox <matthew@wil.cx>]

On Fri, Feb 20, 2009 at 04:24:08PM +0000, James Bottomley wrote:
> I think the point is that it's a transition:  Once it comes out of it we
> either get access or we don't, so it's worth waiting to see what
> happens.

I agree.  If we knew that it could only be transitioning to inactive, we
could skip it.  This state probably only gets returned once in a blue
moon anyway.

> > I don't know what 'Enable Spinup' is for -- maybe Doug knows?  Sending a
> > START_STOP to the device might be exactly what they intend for us to do.
> > Under a 'First, Do No Harm' theory, perhaps we should leave well enough
> > alone and just add Standby and Unavailable?
> 
> As I said, it's a SAS power management command related condition:  The
> drive is limited to consuming a certain level of power and that's not
> enough to spin up, so it won't spin up regardless of how many start unit
> commands it gets sent until the power management control is changed to
> allow it to consume enough power for the spinup.  I think it's ignorable
> for now ... it probably means that when power management is added we
> need to get the transport classes involved to send the appropriate sas
> pm command.

Looking at SAS2r14, I see that NOTIFY (ENABLE SPINUP) is a primitive,
not a command.  If the SAS device is attached through an expander, I
don't think we have a way to send that primitive to the device.  We must
wait for the expander to send it.  If it's sirectly-connected, the
initiator port is supposed to send it.  Presumably this is handled
either by firmware on the HBA or by the HBA driver; either way, we don't
seem to have a way today to get the HBA to send this primitive.

I think our current behaviour is correct for this command, so the patch
here: http://marc.info/?l=linux-scsi&m=123513805527153&w=2 is correct.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."