The concept of MAID technology is the brainchild of a research team from the University of Colorado who hypothesized that MAID (massive array of idle disks) would be a storage structure that would deliver the density of tape with the performance similar to that of disk and with a very small power envelope. SNIA defines MAID as “a storage system comprising of a massive array of (idle) disk drives that are powered down individually or in groups when not required.”
The motivation for such an architecture was to deliver a solution that exploited relatively inexpensive SATA disk technology to create a commercially viable, enterprise class, mass storage solution that exhibited much of the access performance and data integrity characteristics of a disk array but with the economics of a tape library. The sweet spot for this technology, and where it will deliver the most benefit, is in the storage and management of persistent data that is, infrequently accessed data (low IOP’s), data that will rarely if ever be changed, but data that is serving applications that need faster, small grained data access than off-line or even nearline storage can deliver.
But not all “MAID” labeled solutions are created equal and the purpose of this brief is to highlight some unique MAID characteristics and provide some wisdom to those considering the value of MAID or are in the MAID acquisition thought process.
A MAID system suitable for an enterprise data center application is identified by unique design characteristics that are not noticeable in traditional array design.
1.Very high drive packaging density - The fact that in a MAID architecture the number of drives that can spin at any one time is limited. This allows extremely dense packaging not possible in conventional architectures. Example, a single COPAN frame can support up to 896 drives while the new EMC Infiniflex 10000 aka Hulk tops out at 300 drives and DataDirect Networks S2A Storage Scalar at 600 drives per rack. Greater storage density delivers floor space savings, elimination of aging technology through consolidation and the opportunity to reallocate more expensive storage to more appropriate use and potentially delaying an expensive purchase.
2.The number of drives that can spin at any one time is limited and will not exceed 50% of the total number of drives installed. - This is the original definition as presented by the University of Colorado researchers. COPAN currently limits this number to 25%. The key being that not all drives spin at any one time reducing maximum power requirements, reduced heat generation which in turn reduces the necessary cooling infrastructure and aides in the elimination of rotational vibration issues
3.The power available in the Cabinet will not support all drives spinning at any one time. - Limited power budget drives power efficiencies and prevents any misguided attempt to power up all drives.
4.The component count, power supplies, power converters, fans etc will be significantly less than traditional architectures. - Reduced component count should equate to a less cost and improved system reliability. However only actual reliability data will confirm how well theory performs when reduced to practice.
5.Access to data on drives that are powered down will be 15 seconds or greater. Longer than expected from a traditional disk subsystem but significantly less than off board tape. - Applications must be MAID aware. A request for data on a powered down LUN will experience a delayed response back to the application and if the application is not MAID aware the delay may trigger a time out or recovery action. Applications must be MAID aware.
6.To meet data center, enterprise class expectations the solution should have embedded data and device integrity checking and self healing capabilities. - The value and usefulness of data lives much longer after its creation and its initial period of activity. Corporate governance and government compliance regulations are causing data to be stored for increasing longer periods of time and it is this accretive process that is fueling the explosive data growth issue. Any solution that targets the storage of long term data must be architected to ensure the integrity and availability of the data when requested. The more automated the processes the better.
What is not a characteristic of a MAID solution is the increasingly common feature of drive spin down, occasionally referred to as sleepy drives, a software feature added to traditional array architectures. Spin down is a compromise approach enabling vendors to add this feature to existing array architectures. It is better classified as a power efficiency feature that will deliver 25% to 60% of the power savings possible from a MAID implementation. Companies who offer a spin down option include Fujitsu, HDS, NEC, EMC, DataDirect Networks, Nexsan with Pillar Data promising a future deliverable.
Action Item:
- MAID will not replace Tier 1 or Tier 2 storage in mission critical applications or where the data is highly volatile. Leads to point 2.
- Data classification is a critical first step. MAID is not a cover for sloppy data management practices. Understand your data and your migration strategy before including MAID in your storage architecture.
- With the economics of a MAID disk storage solution challenging that of tape consider what data can be migrated from tape. Why? Drive improvements in data access, find-ability and data robustness. In short, deliver a higher QoS for reference, historical, inactive or other types of traditionally labeled Tier 3 and Tier 4 data.
- MAID delivers the highest storage density which can deliver meaningful floor space savings. By consolidating your persistent data onto a MAID platform you open the possibility to reallocate more expensive storage for its intended purpose (highly active, transactional data) and perhaps delay an expensive purchase. Another possibility is the elimination of aging technology, freeing floor space, capturing energy savings and reducing operational expense.
- Expect significant power savings but appreciate what MAID and spin down can deliver.
- MAID and spin down technologies deliver different Quality of Service and environmental advantages.
- Any application that is being used with a MAID device must be MAID aware
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