In banking, healthcare, aviation, communications and other industries around the globe, companies are focused on IT efficiency and reducing their Total Cost of Ownership (TCO). Confronted with budget constraints, pressure to increase service levels, compliance initiatives, concerns about energy consumption and costs, and the ever-present growth of data volumes, efficient operations are an ongoing challenge.

Data growth is usually a result of multiple factors: an onslaught of content creation and consumption; increasing electronic transactions; fat media files; large databases; and a more stringent regulatory environment that requires data to be retained and kept readily accessible for longer periods. This data growth is prompting additional storage purchases for capacity and to improve performance by increasing the number of spindles. This results in storage arrays becoming significantly underutilized, which means wasted capacity and bloated acquisition costs. Hierarchical Storage Management (HSM) migration is an antidote: It can help IT administrators save money on expensive storage and still keep data highly accessible.

HSM Migration

Recently, the IT universe has entertained a constant stream of chatter about the exciting “new” technique of automated storage tiering that virtualization seems to have enabled. However, in the mainframe world, IT users have been leveraging this type of technology since the early ’90s with HSM, which is a policy-based process for moving data from the most expensive, highest-performance storage pool to less-expensive pools over time, while keeping data quickly accessible. HSM originated before the advent of Storage Area Networks (SANs), when both the cost and speed differentials between disk and optical/tape were far greater than today, and when fewer efficiency technologies existed.

HSM migrates data according to IT-defined policies; generally, more active data is kept on the highest tier and less active data is moved to lower tiers. The entry of secondary disk into the data center creates an intermediate disk pool option, and enables a combined pool of disk and tape data that serves as an active archive; data can be backed up but still available online.
HSM is often configured so that as disks reach a certain capacity threshold, files are automatically migrated to another storage pool, but leave behind a “stub” file that identifies file attributes and points to the new location. This stub file ensures quick recall so data access isn’t compromised by the migration. While backup requires a restore request to bring data back, HSM migration keeps data more available. When a user needs a file, the HSM application simply locates it and transparently returns it to the user. Migrations can be initiated on demand, too; for example, to move data that might interfere with backup performance. Other commonly used migration policies are based on data age, most recent usage, size, user, application, etc.

Traditional HSM Migration

The HSM migration process identifies data that hasn’t been recently accessed and moves active data (L0) to migration level 1 (ML1); this data is compressed and stored in a different area on Tier 1 disk. The compression-on-write takes up mainframe CPU cycles, as does the decompression when data is recalled. After a certain period (or other policy threshold), the data is moved typically from ML1 to tape (ML2).

Recalls from tape require the tape to be mounted and sequentially searched to find the right data set; as a result, response times are unpredictable and can take several minutes. Imagine an organization that has 2,000 recalls daily, each taking 90 seconds—that’s 50 hours of lost productivity! In addition, the management of thousands of tape cartridges, the unreliability of tape media in the long term, the massive floor space requirement, and the ease with which tapes can be lost, stolen, or destroyed all give IT administrators pause.

Because mainframes support mission-critical business processes, data availability is paramount; if data managed by HSM is unavailable, multiple corporate divisions or processes can come to a screeching halt. This can impact customer services, revenue, and compliance. For example, if an airline’s HSM migration slows data access, it may affect maintenance tasks, crew scheduling, and any number of processes that impact passenger services. Tape systems restrict flexibility, as tape drives are often directly connected to individual mainframes, requiring complex manual intervention to alter data set access. These tasks create delays that impact productivity.

HSM Migration With Disk-Based Virtual Tape

A dynamic virtual tape disk array can be used to replace physical tape systems and virtual tape servers, offering significant improvements in the HSM migration process. First, it can eliminate tape mounts, robotic activity, rewinds, and the long reads and drive contention problems of tape recycles. In addition, a disk-based virtual tape array can provide gigabytes of throughput per second to speed every tape process, including HSM. By storing each VOLSER as a file on disk, this type of solution minimizes the space required, and typically satisfies recall requests in seconds.

With tape data stored on disk, you can leverage disk-based performance and compression and bypass the first HSM step (L0 to ML1) and go directly from active data to ML2. With recall times typically less than 2 seconds, this saves productive time. This method of HSM migration can reclaim both mainframe host CPU cycles and Tier 1 storage space used for the L0 to ML1 step; this keeps all the processing power available to applications, reduces costs, and frees up computing and storage resources for other tasks. The time savings are significant; using the previous example, those 2,000 recalls would take just over one hour, instead of 50. That type of difference can have a huge impact, helping users get answers faster and improving both customer facing and internal business processes. In addition, tape recycles are faster since stacking is eliminated and all data is on disk.

A Single Solution

A virtual tape disk array can eliminate the challenges of tape handling, such as manual management, physical movement of cartridges, problems with robotics, questionable reliability, and greater risk of tapes being lost, stolen, or destroyed for HSM migration and other tape processes such as backup, work tapes, and data archiving. Optimally, a virtual tape solution that leverages both standard and de-duplication storage in the same device would minimize management, data center footprint, and energy costs. This type of system could direct tape processes to the most appropriate storage; for instance, sending backup to de-duplication storage and HSM migration to standard disk.

As you evaluate disk-based virtual tape solutions, be sure to check on other attributes. For example, will the solution:

• Work seamlessly and transparently with your existing applications and business processes, or does it require code changes, altering production operations or Job Control Language (JCL)?
• Improve performance and shrink batch windows?
• Extend Disaster Recovery (DR) capability to tape workloads with array-based replication?
• Improve data protection with advanced security and encryption features?
• Scale easily without complex re-configuration as workloads grow?


HSM migration provides a method of reducing storage costs by automatically migrating data to less-expensive storage tiers based on policies. The beauty of a disk-based virtual tape solution for HSM migration is that the right solution can do the job without consuming mainframe-processing cycles, using less Tier 1 storage, and keeping data quickly recallable. In addition, virtual tape can bypass the intermediate pool and send data directly from active Tier 1 storage to tape. Disk-based solutions are also faster, more reliable, and improve data protection.