MAID 2.0 products have evolved to incorporate disk spin down

MAID has evolved from being a discrete product category to being incorporated as disk spin down or MAID 2.0 feature sets in storage vendors' disk array products.

By Manek Dubash, Contributor

MAID 2.0 products have evolved to incorporate disk spin down techniques that offer energy efficiency even in a production environment by shutting down some drive functions while they're not being accessed.

Copan Systems was the trailblazer in the MAID products space when the company launched its first such array in 2004. But after a lengthy period of falling sales -- a key problem reportedly being its very densely packed systems proving too heavy for floors at some data centres -- Copan Systems was acquired by SGI early in 2010.

Other vendors later joined Copan in the MAID market. Nexsan brought its AutoMAID technology to the market, offering three levels of savings, each with a tradeoff between access time and energy savings.

Some, such as EMC, have tended to see MAID as a discrete, dedicated product category and prefer the term spin down to describe the feature in its arrays that delivers only a single level of power savings, with disks powered either on or off.

MAID 2.0 and spin down products target tape users

A key target market for MAID 2.0/spin down product vendors are tape users. Tape offers good reliability, an excellent energy consumption profile -- energy costs are zero while it's not being accessed -- and large capacity.

But the disadvantages of tape can be severe. Tape is a linear medium, so retrieving a single file from a tape can be a long process, especially if retrieval is not automated and requires human intervention. Tape has mechanical disadvantages too, occupying much more physical space per gigabyte than disk, and tapes are easily damaged in ways that can result in complete failure of the medium.

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Tape storage trends move at a similar pace to the rest of the storage industry. Bit density doubles every 18 to 24 months, and new drive mechanisms are released that take advantage of that. Data on old tape then needs to be regenerated onto new media unless the organisation decides to maintain its existing generations of tape technology. But that too costs money and creates an admin overhead as it must maintain physical drives, host bus adapters, and the drivers and operating system revisions required to access that data. Given today's compliance and business requirements -- think pension companies that require very long periods of data storage -- this can be a major drawback.

MAID, or massive array of idle disks, is designed to remove the biggest obstacle to the use of hard disks as deep archive storage, namely their power consumption, by spinning the disks down when not in use.

The advantages of MAID over tape are clear: Power consumption when the drives are spun down can be zero or close to it, depending on the type of spin down deployed, while access time remains relatively low, measured in seconds rather than the minutes, hours or days that tape typically provides.

The savings can be large; for example, Copan claimed its MAID systems consumed 11 watts per terabyte compared with a standard array that uses 51 watts.

There can be space advantages too, as inactive disks can be packed much more closely because their cooling requirements are lower. Proponents of MAID have also claimed that disk life is vastly enhanced by being powered down. Copan Systems has said that installation in a MAID array results in a 383% extension of a drive's service life, or 4.8 times greater than the manufacturer's mean time between failures. It concluded that MAID should improve device reliability, and that its studies show an increase in data reliability as measured by mean time to data loss 22 times that of standard SATA RAID arrays and six times that of Fibre Channel RAID arrays.

Although access times for MAID and disk spin down compare favorably with tape, they're not as fast as with spinning disk, and there are concerns about its flexibility. Dedicated MAID arrays, usually SATA-equipped, are normally idle, as the name implies. This means access can take some time, as the drive needs to power up, spin up and perform startup checks before it's ready for access. This can result in a delay of between 15 seconds to 60 seconds, depending on the readiness of the drive.

Such access times -- typical of so-called MAID 1.0 -- are acceptable for some persistent data archiving purposes though not for usages requiring faster access. However, the improved capabilities of MAID 2.0 products now allow spin down-featured products to be used for limited purposes in production environments.

In persistent data applications, however, MAID shares with tape the challenge that data can't be written and forgotten forever. It needs rewriting to disk from time to time, but a competent MAID system will automate that process.

High disk density in arrays, while lessening data centre space requirements, can also be a disadvantage with some users reporting floor loading problems.

A sampling of MAID 2.0 and disk spin down vendors

DataDirect Networks
Max capacity: 11 PB
MAID features: Dynamic-MAID variable spin down

Disk Library 4000 Series
Max capacity: 1.4 PB
MAID features: All-drive SATA disk spin down

Disk Library 5000 Series
Max capacity: 2.7 PB
MAID features: All-drive SATA disk spin down

Clariion CX4 Series
Max capacity: 1.9 PB
MAID features: Policy-driven spin down

Fujitsu Storage Systems
Eternus Series
Max capacity: 2.7 PB
MAID features: Policy-driven MAID/spindown

GB-X Series
Max capacity: 216 TB
MAID features: MAID/spin down

Hitachi Data Systems
Adaptable Modular Storage Systems
Max capacity: 680 TB
MAID features: Optional MAID

Nexsan Technologies
AutoMAID technology in SASBoy, SATABeast, SATABoy and SATABeast Xi products
Max capacity: 84 TB
MAID features: Three-level MAID, sequenced drive spin-up, periodic surface scan

SGI (formerly Copan Systems)
Copan Native MAID 300M (formerly Revolution Series)
Max capacity: 896 TB
MAID features: Maximum 25% of drives on, minimum 75% of drives off, 89.6 TB per sq. ft.

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