Alan,
The FBA command set originally contained support for Reserve/Release.
The IBM 4331 and 4361 processors (direct attach), as well as the 3880-4
controller provided the following related channel commands:
X'14' Unconditional Reserve
X'94' Device Release
X'B4' Device Reserve
Each of these commands returned 24 bytes of sense data.
Use of the commands required the channel switch feature to be installed in
the controller (3880) or the string switch feature to be installed in the
device (3370).
If IBM's simulation of FBA on SCSI lacks Reserve/Release functionality, then
that indicates that the simulation of FBA is not fully implemented. It does
not indicate a lack of functionality in the FBA command set.
John P. Baker
-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On Behalf
Of Alan Altmark
Sent: Thursday, July 03, 2008 3:45 AM
To: IBM-MAIN@BAMA.UA.EDU
Subject: Re: Another difference between platforms...
No. Count-Key-Data describes a *semantic* for accessing data. Many of
those semantics (such as searching) do not apply to FBA. Another example:
There is no RESERVE or RELEASE on in the FBA architecture.
It is trivial to convert CCHHR to an FBA block number.
z/VM, z/VSE, and Linux are able to take advantage of SCSI devices because
their file systems treat the disk as a block device. You won't find
physical FBA
block numbers or CCHHRs in the filesystem interface. File system block
numbers are converted to CCHHR or physical FBA block numbers, or memory
pages, as needed.
But the limitations of the FBA architecture mean that, for example, I cannot
share a RACF/VM database when deployed on FBA. Even if CP's simulation of
FBA on SCSI was updated to include RESERVE/RELEASE, it wouldn't work
because there is no concept of channel path groups and no "lockout"
mechanism in the SCSI controllers.
Alan Altmark
z/VM Development
IBM
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