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Data allocation and in Mainframe server

Posted on 2006-06-10
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Hi ,

How the physical data distribution and data allocation is done in the Mainframe server?

How the logical data seperation is done and how the processes are differed from the general JCL and cobol code?
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Question by:m_razesh
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giltjr earned 125 total points
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Which mainframe?  I am assuming you mean IBM's mainframes.  This is sort of tough to define.  Today the real physical dasd is the same dasd you use on any business class distributed server, that is SCSI drives.   SANs that are compatiable with IBM mainframes emulate IBM's mainframe DASD archicture.  The most recent are the IBM 3390 DASD units.

As with any DASD unit they have tracks and cylinders.  Files are allocated by tracks or cylinders, a cylinder has 15 tracks.  A track has about 50K bytes.  Files are written in "blocks" where a block is about equal to a cluster in the distributed world.  Records are more of a logical idea and based on a file definiton that defines how long records are.  The traditional mainframe file system does NOT use CR or CRLF for end of record markers.  

You can go here and you will find books that introduce you to IBM's z/OS enviroment.

http://www.redbooks.ibm.com/cgi-bin/searchsite.cgi?query=ABCs

I would suggest volumes 1 and 3.

Please note that z/OS has a split personality (at least I look at it that way) when it come to data allocation.  It has the traditional MVS file structure and it also has a Unix type HFS system.
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