The mainframe storage basics cover tape, disk and virtual disk, but the preferred storage media depends on what...
your goal is for the data.
Tape storage options can be particularly challenging for mainframe shops that must balance continuous operation and rapid recovery against the need for cost-effective, long-term storage.
Disk is clearly the predominant storage medium for any modern computing environment. Organizations select from basic storage options -- serial ATA, SCSI attached storage (SAS), Fibre Channel and even solid-state (flash) storage devices -- to achieve an appropriate mix of performance and capacity for the mainframe workloads.
IBM's System z touts the DS8000 series of disk storage subsystems that support replication, storage tiering, quality of service and a hybrid mix of magnetic and solid-state storage devices to provide capacities ranging from 3 TB to 3 PB. This is the preferred approach for working applications and data sets.
The valuable data that is most active in disk storage must also be protected and archived -- not only to ensure business continuity, but also to adhere to regulations, legal discovery and other long-term retention requirements. Data that must be preserved, but is less frequently accessed, is often relegated to a tape storage subsystem.
Virtual tape is a popular approach: Relatively inexpensive, high-capacity disk storage provisioned into logical entities emulates tape volumes. Backup and recovery tools see virtual tape the same as physical tape, but organizations benefit from disk's better performance for fast recovery point and recovery time objectives.
For IBM System z mainframes, the IBM TS7720 virtualization engine caches data to 3 TB SAS drives organized in RAID 6 (dual parity) groups for storage resilience. The TS7720 is rated for over 1,500 virtual tape drives encompassing 4 million virtual volumes. Mainframe storage administrators can replicate virtual disk volumes and protect them using other disk storage techniques -- even write the volumes to actual tape.
From a practical standpoint, physical tape storage is obsolete as a working mainframe storage medium. No modern enterprise tolerates the downtime to back up or restore workloads and data from tape. However, expanding regulatory and legal obligations demand that organizations retain increasing volumes of data for longer periods of time -- even when that data is not actively used. This kind of long-term archival storage remains a perfect use case for physical tape. The System z can use IBM's TS1140 tape drive to archive from 500 GB to 4 TB per cartridge at burst data rates of 800 MBps. The TS1140 also supports encryption and key management to safeguard sensitive data on tape.
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