IBM SG24-5360-00 manual Data Compression and Compaction, Functional track table

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The functional track directory (FTD) is the collective name for two tables that together map each functional track to an area in the RVAs physical storage:

Functional track table

The functional track table (FTT) contains the host-related pointers, that is, the functional-device-related track pointers of the FTD.

Track number table

The track number table (TNT) contains the back-end data pointers of the FTD. A reference counter is also part of this table.

Although the FTD consists of two tables, we discuss it as one entity (see Figure 1). In fact, each functional track has an entry in the FDT. If a functional track contains data, its associated FTD entry has a pointer to the FBA block where the data starts. The data of a functional track may fit on one or more FBA blocks.

If the data of a functional track is updated, the RVA puts the new data in a new place in the log structured file, and the FTD entry points to the new data location. There is no update in place.

Figure 1. The RAMAC Virtual Array Tables

1.1.3 Data Compression and Compaction

All data in the RVA is compressed; compression occurs when data enters an RVA. In addition, the gaps between the records, as they appear on the CKD devices, are removed before the data is written to disk. Similarly, the unused space at the end of a track is removed. This is called compaction. The compression and compaction ratio depends on the nature of the data. Experience shows that RVA customers can achieve an overall compression and compaction ratio of 3.6:1.

Data compression speeds up the transfer from and to the arrays. It increases the effectiveness of cache memory because when compressed more data can fit in cache.

2 RAMAC Virtual Array, Peer-to Peer Remote VSE/ESA

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Contents International Technical Support Organization Page International Technical Support Organization First Edition January Contents Peer-to-Peer Remote Copy Itso Redbook Evaluation Contents Vi Ramac Virtual Array, Peer-to Peer Remote VSE/ESA Preface Team That Wrote This RedbookComments Welcome Your comments are important to usWhat Is an IBM Ramac Virtual Array? IBM Ramac Virtual ArrayOverview of RVA and the Virtual Disk Architecture Log Structured FileData Compression and Compaction − Functional track tableWhat Is IXFP/SnapShot for VSE/ESA? What Is SnapShot?VSE/ESA Support for the RVA What Is IXFP? Deleted Data Space ReleaseWhat Is Peer-to-Peer Remote Copy? Reporting FunctionsRamac Virtual Array, Peer-to Peer Remote VSE/ESA RVA Benefits for VSE/ESA RVA Simplifies Your Storage ManagementDisk Capacity Administration IxfpBatch Window Improvement Ramac Virtual Array IXFP/SnapShot for VSE/ESAApplication Development RVA Data AvailabilityHardware SnapShot PprcRamac Virtual Array, Peer-to Peer Remote VSE/ESA VSE/ESA Support for the RVA PrerequisitesVolumes 1 VSE/ESA Input/Output Configuration ProgramHost Connection Volume Minimal Init Partial Disk Minimal InitAssgn ExecRamac Virtual Array, Peer-to Peer Remote VSE/ESA IXFP/SnapShot for VSE/ESA System VSE/ESA User TimeDTRIATTN,PARM=′ Ixfp REPORT′ Sample Batch Job to Invoke Ixfp Report FunctionIXFP/SnapShot for VSE/ESA Detail PhysAR 0015 CUU DEF DefinedFull Volume Ixfp SnapReply ′ YES′ to Proceed VSE/VSAMRange of Cylinders Non-VSAM File Expired Files Total Volume Ixfp DDSR,PATEV3Ixfp DDSR,PATEV30000-0999,NOPROMPT Specified File Ixfp DDSR,PATEV3DSN=′ test.data.3′ , NopromptIxfp REPORT,80E Ixfp REPORT,80F Ixfp REPORT,80E,80FIxfp Report Sample Output of Ixfp Report Command Device Detail ReportRamac Virtual Array, Peer-to Peer Remote VSE/ESA Device Summary Report Subsystem Summary ReportRamac Virtual Array, Peer-to Peer Remote VSE/ESA Peer-to-Peer Remote Copy Peer-to-Peer Remote CopyPprc and VSE/ESA Software Requirements Pprc Data FlowPprc Hardware Requirements Invoking peer-to-peer remote copyExamples of Pprcopy Commands SnapShot ConsiderationsPrimary Devices of a Pprc Pair Secondary Devices of a Pprc PairSetting Up Pprc Paths and Pairs Recovering from a Primary Site FailureRecovering from a Secondary Site Failure Deleting Pprc Pairs and PathsPhysical Connections to the RVA Determining the Logical Control Unit Number for RVA Determining the Channel Connection AddressRamac Virtual Array, Peer-to Peer Remote VSE/ESA Appendix A. RVA Functional Device Configuration Functional Device ConfigurationFunctional Device Configuration Screen CD23 Appendix B. Ixfp Command Examples Snap CommandSyntax Ramac Virtual Array, Peer-to Peer Remote VSE/ESA Using SnapShot to Copy One Volume to Another NopromptAR 0015 Capacity DEFINED-CAPACITYTest Prod Overall Test Prod Using SnapShot to Copy a File from One Volume to Another Using SnapShot to Copy Files with RelocationOther Uses of SnapShot IXFP20I Snap Function Completed ATDdsr Command Syntax of Ixfp Ddsr Command DetailsUsing Ddsr to Delete a Single Data Set Using Ddsr to Delete the Contents of a VolumeUsing Ddsr to Delete the Free Space on an RVA ReportAR+0015 IXFP29D Ddsr for For Deletion Report Command Reporting on the Capacity of a Single Volume Reporting on the Capacity of Multiple VolumesReporting on the Capacity of the RVA Subsystem Device Detail Report FUNC. Capacity MBIXFP/SnapShot Setup Job Streams JOB WCWTEST1Exec DTRIATTN,PARM=′ Ixfp REPORT′ BG 0000 // JOB Initdisk BG 0000 1A86I Following Assignments are ReleasedIxfp DDSR,80E Ready Ixfp DDSR,80F50.83 47.86 AR 0015 1I40I Ready $$DITTO BLKFACTOR=1 EOJ$$DITTO BLKFACTOR=1 $$DITTO EOJ 726532.208 MB 117880.209 MB 57754.953 MB Appendix C. VSE/VSAM Considerations Backing up Vsam Volumes Appendix C. VSE/VSAM Considerations Ramac Virtual Array, Peer-to Peer Remote VSE/ESA Appendix D. Iocds Example Ramac Virtual Array, Peer-to Peer Remote VSE/ESA Appendix E. Special Notices Following terms are trademarks of other companies Appendix F. Related Publications International Technical Support Organization PublicationsRedbooks on CD-ROMs Other PublicationsRamac Virtual Array, Peer-to Peer Remote VSE/ESA How to Get Itso Redbooks ∙ E-mail OrdersIBM Redbook Fax Order Form Please send me the followingIndex See CKDPprc distance Itso Redbook Evaluation Please answer the following questionsSG24-5360-00