Re: [PATCH 1/3] sd: don't bother spinning up disks on resume

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On Thu, 2013-11-07 at 16:16 -0500, Phillip Susi wrote:
> On 11/7/2013 1:21 PM, Douglas Gilbert wrote:
> > On 13-11-06 08:57 PM, Phillip Susi wrote:
> >> Don't bother forcing disks to spin up on resume, as they will do
> >> so automatically when accessed, and forcing them to spin up slows
> >> down the resume.  Add a second bit to the manage_start_stop flag
> >> to restore the previous behavior.
> > 
> > SCSI disks when in STOP state do not spin up "automatically when
> > accessed".
> 
> The drive does not, but the scsi error handling notices when a command
> fails because the drive needs started, starts it, and retries the command.

No disk does, neither SCSI nor ATA.  The error handler is not
automatically activated for a not ready/initializing command required
because of multi-path.  We override the default behaviour via
allow_restart only for IBM vfc/vscsi and ATA disks.  With this patch
SCSI devices would no longer ever restart after suspend.

> > And your choice of bits looks like it will favour fixing broken
> > SATA behaviour but as a by-product break working SCSI disk
> > behaviour.
> 
> No, it has nothing to do with sata behavior; it has to do with whether
> or not all disk drives should be restarted immediately after a resume,
> or only when they are accessed.  I happen to have a few older drives
> that I very rarely access and would rather they not start up every
> time I resume.

As Doug said, if you don't restart a SCSI device after resume, it will
never get started.

James


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