Originating Author: Nicholas Allen
While vendors have done a great job of confusing the market, according to SNIA, Massive Arrays of Idle Disks (MAID) is “A storage system comprising an array of disk drives that are powered down individually or in groups when not required. MAID storage systems reduce the power consumed by a storage array.”
MAID systems generally fall into two categories: Those that can power all the disks at the same time and those that can’t. While the latter, with Copan being the leader, offer the most power savings, some users will find more comfort with the knowledge that, if needed, all the disks can be operational at the same time for, say, for example, a full data restore. The sweet spot for Copan-like MAID is applications or data that do not require performance in terms of IOPS or bandwidth and that need faster access to individual files than magnetic tape can provide together with associated energy savings. However, for sensitive time and large bandwidth operations including DR or full database restore, tape or regular disk can be a better approach.
The industry is evolving past the first generation of MAID systems adding intelligent power management (IPM) features that exploit the new power saving features now being introduced into enterprise-class drives and first implemented in laptop drives. So, users can have different levels of MAID with different power savings and response times. That said, most second generation systems still simply power off select drives. Why? Because it is difficult for a storage subsystem to classify the data. Nonetheless, users can expect more vendors, including mainstream suppliers, to offer tiered MAID storage.
When MAID technology is being considered, users must still classify their data and try to match it to the right MAID technology as follows:
- Align MAID technology, including MAID level, to the applicable tier and application needs.
- Understand the performance tradeoffs of using MAID as an alternative to traditional disk and tape.
- Look beyond energy savings and factor in cost of acquisition and site prep along with TCO and ROI.
- If using MAID for backup, investigate how much sustained throughput the system can handle – especially for restores.
Another opportunity to consider is to make applications storage latency aware. One recent example of this is a major credit card processor that stores 6-months worth of statements online but allows the customer to request statements that are older. That request takes up to 24 hours to fulfill. Clearly the older statements are on offline or nearline storage. If MAID were employed, the request could probably be satisfied in minutes or less, resulting in a better customer experience. Note that after 9/11, many users made the applications aware of the storage topography, i.e., that there is a mirror at another site, so it is not inconceivable that more applications will become aware of various storage latencies and even exploit them.
Action Item: Given performance or other service requirements, not all storage or data applications lend themselves to MAID. However, given the compelling energy savings and asset life extension possibilities of MAID, users should consider it, albeit very carefully.