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[dm-devel] Re: [PATCH 7/9] scsi_dh: Add support for SDEV_PASSIVE

James Bottomley <James Bottomley HansenPartnership com> wrote:
> On Wed, 2008-01-23 at 16:32 -0800, Chandra Seetharaman wrote:
> > Subject: scsi_dh: Add support for SDEV_PASSIVE
> > 
> > From: Chandra Seetharaman <sekharan us ibm com>
> > 
> > This patch adds a new device state SDEV_PASSIVE, to correspond to the
> > passive side access of an active/passive multipathed device.
> Really, no; this isn't right.  The state field of a SCSI device is for
> the SCSI state model.  Passive might be a valid device mapper state, but
> it's not a valid SCSI state.  If these patches can't work except by
> mucking with the SCSI state model, there's some layering problem
> elsewhere that needs sorting out.

It is actually a valid state for this device and a number of other
devices that have passive / active controller. There are differences in
response capability (i.e., media access commands) on certain sds until a
fail over command is given. The response behavior difference along with
all the partition scanning and other commands that get generated during
the probing of a device are what leads to the long boot times previously
mentioned by Chandra.

Since we have created a policy to remove the vendor specific multipath
drivers that handled the aggregation of the paths into a single device we
need some method to handle devices that are not fully capable, but are
still expose to the upper layers.

The patches are also addressing a long standing issue of sense data
processing, but that is not related to the SDEV_* state comment.

Michael Anderson
andmike linux vnet ibm com

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