Mainframe Storage: The Basics

Mainframe Storage: The Basics

Storing data is crucial to an enterprise, but the days of buying additional storage for each new request are gone. The money simply isn't there. IT divisions are being asked to restrict how storage resources are used by their various applications and end users.

Reductions in the work force have depleted much of the knowledge base required to manage storage effectively. The mainframe environment has been especially hard-hit.

This guide should help you bridge that knowledge gap.

The Need for Storage

The information you use for your day-to-day operations has to be safely guarded. To comply with legal requirements, businesses also need to keep records and data files. All of this must be backed up at regular intervals. Determining what to back up and archive – and which media to put it on – can be a full time job.

The storage media you use will depend on what your goal is for the data concerned.

Magnetic Tape

For a modern enterprise, the downtime required to backup or restore workloads and data from magnetic tape can be intolerable.

But regulatory and legal obligations may demand that you retain increasing volumes of data for longer periods of time – even if that data isn't actively used. This kind of long-term archive storage is ideal for physical tape.

System z can use IBM's TS1140 tape drive to archive from 500 GB to 4 TB per cartridge. The TS1140 also supports encryption and key management to safeguard sensitive data.

Sharing Options

Portioning up a tape drive for multiple systems may reduce the need for new drives. Tape storage can even be shared across multiple mainframes.

IBM tape storage can be shared via its Tape Controller Model C07 for System z mainframes. System z can also employ TS1140 tape drives or other products in combination with tape controller subsystems to deploy multiple high-capacity tape drives for intense storage applications.

Disk Storage

There are several reasons to store data files on disk with unattended operation being key. As disk storage devices are always online, jobs can basically run unattended unless a problem occurs.

A huge number of files can be stored on a single disk device with little wasted space. Files can be accessed and opened near-instantaneously. It's not necessary to scan past several other files to reach the desired one, as you do with tape files.

Disk devices can be accessed by many programs simultaneously, with generally little performance impact, effectively eliminating scheduling bottlenecks.

You can select from basic storage options: serial ATA, SCSI attached storage (SAS), Fiber Channel, or solid-state (flash) storage devices. The aim is to achieve an appropriate mix of performance and capacity for mainframe workloads.

DASD

DASD is an acronym for Direct Access Storage Device, a term coined by IBM for any type of storage that was directly (randomly) addressable. It's now applied to any disk drive.

For System z, IBM's DS8000 series of disk storage subsystems support replication, storage tiering, quality of service, and a hybrid mix of magnetic and solid-state storage devices, to provide capacities ranging from 3TB to 3PB. These are preferred for working applications and data sets.

Virtual Tape Systems

Mainframe virtual tape consists of magnetic tape file images stored on disk. High-capacity disk storage is translated into logical entities, to emulate tape volumes. Backup and recovery tools see virtual tape the same as physical. And organizations can benefit from the disk's better performance for fast recovery points and recovery times.

Hardware-based Virtual Tape Systems (VTS) use dedicated special purpose Raid storage, to house the virtual tape images.

Software VTS will intercept I/O requests intended for tape devices, and redirect them to mainframe DASD, instead of mainframe tape. These systems are relatively inexpensive and provide unattended operation. Some use compression to minimize the use of the more expensive mainframe DASD.

LPARs

An LPAR (Logical Partition) is a type of virtual machine implemented by PR/SM (Processor Resource/System Manager) – a hardware/firmware feature on all recent mainframes. System resources (memory, processors, and I/O devices) can be divided or shared among many LPARs, under the control of the LPAR hypervisor. The hypervisor is a software layer designed to manage multiple operating systems running in a single central processing complex.

Each LPAR supports an independent operating system (OS) loaded by a separate initial program load (IPL) operation. Today’s machines can be configured with up to 60 such logical partitions.

Parallel Sysplex

Parallel Sysplex is a clustering technology, which allows up to 32 systems to be operated as a single system image. If properly implemented, even the complete catastrophic loss of a single system can be tolerated without any loss of work. Any work that was being performed on the failed system can be automatically restarted on a surviving system.

One or more systems can be removed from the Sysplex for hardware/software maintenance, while the remaining ones continue processing the workload. When the off-hours maintenance activity is complete, the system(s) can be brought back into the Sysplex. So, you can upgrade software levels on the entire Sysplex without causing any application outage.

Automation

Developing an in-house storage solution can take months or years to perfect. The ideal is to pick a comprehensive toolset that manages storage related resources: data allocation, backup and archiving, performance, physical and logical makeup of the disk, future capacity and tape (virtual and real). Automation is paramount to reduce operator dependence.