No matter what the size of a disk array is in most applications, finding ways to decrease or eliminate wasted resources is a common challenge.
Improving the power utilisation of storage disks can be done by switching components to a low-power consumption mode or a power-down state when not in use. The most common array technology to improve energy efficiency by reducing power consumption is Massive Arrays of Idle Disks (MAID) technology.
The working principle of MAID storage is to turn hard disks (that do not receive access requests for some time) to a low-power state, thereby savingenergy and prolonging the service life of the disks.
MAID storage is suitable for hierarchical storage and large-capacity, near-line storage that has low-access frequency and low requirements on immediate data availability. It also provides excellent data backup for data recovery and data filing.
The MAID array often comprises hierarchical storage such as fiber channel (FC) disks, SAS disks, and SSD disks (flash disks) which are of a higher cost and provide the fastest speed of access, as well as SATA disks that are used as post disks to reduce power consumption.
Flash SSD increases the bandwidth and throughput of hard disks by a factor of five (and sometimes more), reduces power consumption to less than 3W, and can boost energy efficiency of mechanical disks by two orders of magnitude.
MAID technology is able to decrease the total amount of power used by a disk array by more than 30 percent. More importantly, by turning disks to a power-off state, the effective service life of the disk is prolonged and equipment reliability is improved.
The enhanced utilisation of data is largely about applications and software. Generally, more than 50 to 80 percent of disk arrays are either idle or duplicated. This is especially the case with mail servers where duplicate data can account for more than 90 percent of the total volume of data.
Utilising data de-duplication in disk arrays can produce results that cannot be achieved with most other solutions to improve energy efficiency. The underlying principle of data de-duplication technology is to compare data stored in a disk array, and if two identical data blocks are found, only one data block and one tag needs to be stored in the array.
The higher the data de-duplication rate, the higher the efficiency of the data. Data de-duplication can reduce the data storage rate by 50 times. This means that by applying data de-duplication, two disks can do the same work as an array consisting of 100 hard disks – resulting in savings that is hardly achievable with any other technology.
In summary, the following are eight effective measures for decreasing the power consumption of disk arrays:
* Using hard disks with greater capacities
* When system performance allows, minimise the read-write frequency of the hard disks
* When system performance allows, decrease the read/write bandwidth of the hard disks
* When system performance and reliability allows, replace FC disks and SAS disks with SATA disks
* Use 2.5-inch hard disks
* Use a low-power CPU
* Adopt MAID technology
* Adopt data de-duplication technology
Shabir Satar, product manager, Huawei Symantec
