Device Sharing

Gary A. Hoffman gary.hoffman at
Wed Feb 26 07:38:06 PST 1997

* From the SCSI Reflector (scsi at, posted by:
* "Gary A. Hoffman" <gary.hoffman at>
g'mornin Dave,

Something you might want to look at here also ..
SBP-2 has defined (what might be a different way)
a methodology for device ownership.


At 08:29 AM 2/26/97 CST, Dave Peterson wrote:
>* From the serial_solutions Reflector, posted by:
>* dap at (Dave Peterson)
>* To post to this Reflector, send email addressed to
serial_solutions at
>Hello All,
>The purpose of this message is to generate discussion about the sharing
>of devices (specifically tape transport's) between multiple host's and to
>convey the need for consistency between the various standard bodies
>regarding the usage of reserve and release.
>The sharing of transport's is becoming more desirable as companies migrate
>"open system" machines to the traditional glass house for data and storage.
>In the open system arena there is no consistent or well-defined method
>to share a tape device. Tape devices have reserve/release commands to
>facilitate sharing, but few (if any) device drivers
>issue a reserve at open and a release at close. Basically it is left to
>the application.
>The SCSI-2 spec (at least the one I have) states that the reserve and release
>commands are mandatory for sequential devices. After looking at SSC rev 9 I
>noticed the reserve and release commands are now optional for
>sequential-access devices. Currently PLDA_18 requires reserve and release
>for sequential-access devices.
>I believe reserve and release should be mandatory for sequential-access
>devices and device driver's should issue a reserve at open and release at
>The ability to detect the device is already reserved at open and not release 
>the device at close time (int the device driver) would also be beneficial 
>for applications that open and close the device multiple times during it's
>With the advent of Fibre Channel and SCSI-3 I believe now is a good time to
>address these issues.
>Dave Peterson           phone : 612-391-1008
>Senior Engineer 
>Network Systems Corp.	email: dap at

gary a hoffman
Skipstone, CEO
512.305.0200 main             Skipstone Is 1394
512.305.0212 fax
gary.hoffman at    3925 West Braker Lane, Suite 425      Austin, Texas 78759          USA
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