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There are five mainframe suppliers of z/OS virtual tape. The three traditional suppliers are IBM with its Virtual Tape System (VTS), Oracle with its Virtual Tape Storage System (VTSS) and Fujitsu-Siemens. The Fujitsu Eternus C8000 series is unique in that it supports both z/OS mainframes and Open Systems.
The IBM mainframe offering is the TS7700. This comprises a virtual tape grid system with synchronous replication and automated fail-over. The cluster currently has six nodes, but the architecture can support up to eight. The management is an integral part of the VTS and the intelligence is outboard of the mainframe servers. This means that the location and number of virtual volumes are virtualised, which will assist with content-based access. It is possible that IBM will add tape data indexing to the tape grid in future, outboard from the mainframe.
The IBM TS7720 is a VTH solution. It uses 3 TB SAS disks in a RAID 6 format, with a total potential capacity of 6,048 TB. It also has the option to backend this data with physical tape drives.
The IBM TS7740 is a VTA solution. It uses 600 GB SAS disks in a RAID 6 format, with a total potential capacity of 169TB. The TS7740 always has backend tape drives.
Both models can connect to TS1150 or 3592 tape drives in an IBM TS3500 tape library and both support 8 Gbps IBM FICON.
The Oracle / StorageTek offering is the VSM-7. The new feature that Oracle has brought in with the VSM-7 is cloud connectivity. The backend configuration can be three tier, with a disk cache, a physical tape layer and finally a cloud layer. An alternative is to define a two tier system with just a disk cache that feeds into a cloud backend. Oracle claims that this will give you a mainframe virtual tape system with unlimited storage.
Oracle has adopted a modular approach to mainframe tape virtualisation, the four modules being: tape libraries, tape drives, virtual tape disk buffers, and software. This means that most of the logic and intelligence is still held on the mainframe. The VSM uses two Sun SPARC M7 servers for the disk cache and just comes as a 2 node cluster. It uses FICON for tape drive connection and Ethernet IP for replication. The VSM uses triple parity RAID to protect the high capacity drives from failure.
The controlling software is z/OS host-based, and Oracle claims that this gives them enormous scalability, with up to 256 VSM systems as a single image.
The VSM supports both synchronous and asynchronous replication of virtual tape volumes within a clustered VSM environment with VSM4 and upwards. Synchronous replication means that the data must be stored in both VSM caches before the virtual tape drive completes the rewind/unload command and passes control back to the application.
Both Asynchronous and Synchronous replication modes can be used simultaneously in the same VTSS by assigning tapes to different SMS management classes.
Fujitsu sells the virtual tape system which was previously known as CentricStor, which was renamed to ETERNUS CS High End in 2009 (when the Joint-Venture ended and Fujitsu Siemens Computers became FUJITSU). Again in 2013 the appliance was renamed to ETERNUS CS8000. This supports a great range of existing mainframe and major Unix and Windows operating systems as well as major tape libraries, all in parallel with one single system if required. Furthermore ETERNUS CS8000 combines VTL and the NAS option to consolidate backup, archiving, compliant archiving and second-tier file storage in one appliance. It is possible to cluster two VTLs in different sites and mirror the disk cache between them, this giving robust remote disaster recovery.
The CS8000 comes in 3 models, the CS8200 scale-up model, the CS8400 scale-out model and the CS8800 scale-out-split-site model.
Dell EMC offers disk only virtual tape solutions that work on the following principles:
Software that emulate real tape drives
Large amounts of disk storage
An outboard processor to manage them all
EMC bought out Bus-tech, a virtual tape company that produces the Mainframe Data Library (MDL), another VTL solution. The DLm libraries can hold both mainframe and Open Systems data. It can be back-ended with a DMX disk subsystem or a data domain storage unit, which gives a lot of flexibility and capacity.
Just for completeness, some vendors offer a software only solution. An example is CA with its Brightstor product.
The following table describes the Oracle VSM 6 system, an IBM TS7700, a Fujutsu CS8400, an HDS VTF and an Dell EMC DLm 8000. The table includes the terms used by each supplier to describe the components.
|Oracle VSM 6||IBM TS7740||Fujitsu CS8400||Dell EMC DLm 8100|
|Maximum number of virtual drives||512 on a single VSM||256-1536 (these numbers refer to 1 or 6 node clusters, the 7740 can have any number of nodes between 1 and 6 and so scales appropriately)||1280||2048|
|Maximum number of virtual volumes in one virtual tape system||100,000 active in the VTSS cache, no effective limit for VTVs migrated to MVCs; Virtual Tape Volume (VTV)||4,000,000; Virtual Volumes||1,500,000; Virtual Volumes||unlimited|
|Back end storage||32 drives per VSM, called Real tape Drives (RTD) of T10000B or T10000C; Tapes are called Multi-Volume Cartridge (MVC)||16-96 tape drives of TS1150, TS1140, TS1130 or TS1200. Tapes are called "Stacked Cartridge"||112 tape drives in 10 Libraries, IBM, Oracle, DLT drives supported.||Backend is disk only and can be EMC VMAX, or EMC Data Domain, or a combination of the two.|
|Server Support||z/OS variants||z/OS variants||z/OS + various UNIX, LINUX and Windows||z/OS variants|
|Library Support||Oracle libraries||IBM libraries||Fujitsu, IBM, Oracle, Quantum libraries||Disk only, but can support Data Domain virtual tape libraries|
|Maximum disk cache capacity||825TB native using 8TB HDDs. will scale up to 211 PB over 256 systems; Virtual Tape Subsystem Buffer (VTSB)||1,008 to 6,048 TB; Tape Volume Cache||7.2 TB - 22.272 PB; Tape Volume Cache||3.1 PB, 22.8 PB with Data Domain storage|
|Controlling Software||HSC software runs on z/OS Host||AIX based Virtual Tape Controller software, within the VTS.||Eternus Software runs within the VTS.||EMC z/OS Storage Manager|
|Connectivity||8 * 16Gb FICON between host and tape drives.
4*Gbe and 4*FC for replication
|8-48 * 8Gb FICON to RTDs.||4-40 FC 16 Gb / FICON 8 Gb||16 8Gb FICON|
|Scalabilty||As the controlling software and database is in the Host, up to 256 VSMs can be clustered together, and this will appear to be seamless to the z/OS operating system, so scaling from 1.2PB to 409PB assuming 4:1 compression. The backend tape drives are located in an STK siloplex, which has almost unlimited capacity||Two VTS systems can be defined to one TS3500 tape library.||Fujitsu states that the grid architecture makes the device extremely scalable, with the CS8200 being a scale-up system and the CS84000 a scale out system.||Limited to VMAX capacity, can be extended by interfacing to Data Domain libraries|
|Mirroring capability||Either synchronous or asyncronous||A combination of aynchronous (tape rewind not issued until both virtual tape copies are written) and asynchronous, as selected by DFSMS policies.||Asynchronous replication and synchronous mirroring. The CS8800 provides comprehensive 2 site mirroring support.||Uses Synchronous SRDF to mirror between VMAX subsystems|
|GDPS support||Full support, no additional scripting needed||Yes, VTS can be fully integrated into GDPS, so second site tape work would be 'frozen' if there was a problem at the primary site||No data||No, but utilises EMC's GDDR software instead|
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