> -----Original Message----- > From: Linux on 390 Port [mailto:[EMAIL PROTECTED] On > Behalf Of Alan Altmark > Sent: Friday, October 07, 2005 12:15 AM > To: LINUX-390@VM.MARIST.EDU > Subject: Re: SCSI and CKD >
<snip> > A nice question for z/OS, VSAM, and DB2 experts. > > Alan Altmark > z/VM Development > IBM Endicott I am not a z/OS, VSAM, or DB2 expert. But I am the senior z/OS person here at work (started working with OS/VS1) and I am at least generally familiar with them. VSAM does not use hardware keys. It is composed of fixed length "Control Intervals" which are composed of one or more fixed blocks on DASD. It could be considered "FBA compatable". There are a set of possible "Control Intervals" for a VSAM file. Each "Control Interval" in a given VSAM file is the same length. This is true of all types of VSAM files (KSDS - keyed, ESDS - sequential, LDS - "page like", RRDS - access by relative number record with fixed length records, VRRDS - access by relative record number with variable length records). I am fairly sure that DB/2 uses LDS VSAM files. LDS files are 4K Control Intervals. They act somewhat like private "page dataset" since I/O to them is done by "mapping" the dataset into memory (possibly windowed). Or using the undocumented (to us "unwashed masses") Media Manager I/O interface. IMS can use VSAM or OSAM. OSAM are also fixed blocked files with no keys. That means that they are "FBA compatable". To the best of my knowledge, there are only two types of datasets on z/OS which actually require ECKD funtionality. The old style PDS (BPAM) which use hardware keys in the "directory" portion of the dataset. This is the major sticking point for z/OS. These types of datasets are used very early in the IPL process and replacing that code is said (by IBM people on IBM-MAIN) to be "difficult". IBM is slowly replacing PDS with PDSE. PDSE files look like VSAM under the covers (4K fixed blocked, logical records / blocks are emulated by the access method). The other type of dataset is keyed BDAM. IBM has "functionally stablized" BDAM and is deemphsizing it (CICS no longer supports it). Non-keyed sequential files could be replaced by a ESDS type organization. OEM products may still use this. -- John McKown Senior Systems Programmer UICI Insurance Center Information Technology This message (including any attachments) contains confidential information intended for a specific individual and purpose, and its' content is protected by law. If you are not the intended recipient, you should delete this message and are hereby notified that any disclosure, copying, or distribution of this transmission, or taking any action based on it, is strictly prohibited. ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
