Automated storage tiering strategy: Inter-array tiering

What you will learn in this tip: Automated storage tiering (AST) can be implemented in two ways: Intra-array tiering and inter-array tiering. Learn about the different vendors

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that offer inter-array tiering in their products to help you determine if it's the right AST strategy for your data storage environment.

Storage tiering review

Most IT professionals generally understand storage tiering, but it’s worth a brief review of the concept. Tiers are defined predominantly by the performance characteristics of the underlying media. Solid-state drives (SSDs) and flash memory are referred to as tier 0; high-speed Fibre Channel (FC) drives such as 15K rpm disks are tier 1; 10K rpm FC and SAS disks are tier 2; and less than 10K rpm SATA disks are tier 3. These aren’t absolute rules, but they’re typical tier differentiators.

Tiers are implemented in two different ways. The first is intra-array, in which a single array is populated with two or more media types. The second is inter-array, in which arrays with different media types are associated to facilitate data movement. It’s also possible to have both simultaneously in the same configuration.

Inter-array tiering

Hitachi Data Systems’ (HDS) AST supports the same tool set across all product lines for inter-array tiering. It begins with virtualization to abstract and partition workloads. In fact, HDS recommends application and workload classification rather than data classification. “Organizations should avoid starting out too complex in their tiering strategy,” said Sean Moser, vice president of software at HDS. “Don’t use too many tiers and over-optimize individual applications.” Although HDS supports three tiers, as a practical matter the middle tier becomes a “shock absorber” between higher and lower tiers.

HDS offers a Data Center Management suite that includes configuration management, tuning management and tiered storage management. It provides alerts and a dashboard that gives details by volume, storage pool, service-level agreement (SLA) and peak periods. Using these tools, users can fine-tune the system over time. HDS can also incorporate other vendors’ arrays into the storage pool whereby older systems can be repurposed and used as a data archive. HDS can use spin-down drives for the archive tier to reduce power and cooling requirements.

Hewlett-Packard (HP) Co. is more traditional in its approach to automated storage tiering. Perhaps because some of its arrays come via a partnership and acquisitions, the AST capabilities vary between product lines. Its high-end P9500 systems, OEM units from HDS, behave very similarly to HDS’s AST implementation, and you can use the P9500 to virtualize other arrays.

HP’s 3PAR product line is a relative newcomer to AST, having rolled out those capabilities approximately a year ago. 3PAR supports three tiers, but it’s largely up to users how to configure them. HP recommends monitoring the applications for usage patterns and then determining what tiers at what sizes to implement. Its Adaptive Optimization tool is available to help with the monitoring and sizing of tiers.

HP’s x9000 scalable NAS uses its own AST as well. In this case, all policies are user generated. HP says automated storage tiering evolves from user policies to automation over time.

IBM’s Easy Tier product is supported on its Storwize V7000, DS8700, DS8800 and SAN Volume Controller products. Currently, Easy Tier supports two tiers, one of which must be solid-state drives. Once every 24 hours, the product analyzes performance metrics and generates a plan to relocate data appropriately. Data relocation occurs in 1 GB extents, which are migrated no more often than every five minutes to avoid performance interruption. Easy Tier is a function of the array and is a no-cost option.

Automated tiering market still developing

The good news about automated storage tiering is that the market is robust with many options. The bad news is that the options make comparing implementations rather bewildering. Jerome Wendt, lead analyst and president at DCIG in Omaha, Neb., has some practical advice for evaluating the appropriate solution. “First, users should match the performance needs of the application to the architecture of the product,” he said. “This includes understanding the size of the data block being moved, how often it’s being moved and how it’s moved between tiers.” Wendt further advises that file systems are fairly safe candidates for AST, but that Microsoft Exchange and databases should be approached more cautiously.

For more information on automatic storage tiering, read part 1 of this tip series, “Automated storage tiering options for your environment.

BIO: Phil Goodwin is a storage consultant and freelance writer.

This article was previously published in Storage magazine.


This was first published in July 2011

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