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The revolution in hard disk drive storage: small 2.5" serial attached SCSI drives.

Big changes are coming for the hard disc drive market. As demand grows for disc drives in the consumer electronics industry, an equally robust demand is driving major changes on disc drive products in the enterprise server market.

Enterprise servers have long used the standard parallel SCSI 3.5" hard disc drives for internal storage requirements. Ever-increasing demand for data storage is causing drive manufacturers to re-evaluate the way storage is architected. Parallel SCSI interface technology has reached its maximum potential and is becoming a bottle neck to data processing. The problem comes from multiple disc drives sharing the available data bus bandwidth, which limits the throughput and can slow transaction on intensive applications. This problem becomes exacerbated by the huge growth of reference and transactional data throughout the industry. Transactional data is defined as mission critical information that is utilized daily, and must be accessible 24 hours a day. Conversely, reference data is information that is stored once and accessed infrequently.

Some IT experts expect there to be more data created and stored in the next 5 years than at any time in the history of the world. Requirements like these for large volume data storage, compounded by fast query requirements are stretching the processing capability of parallel SCSI technology. The only answer is to change the protocol for accessing data from disc drives--enter Serial Attached SCSI, or SAS. By transitioning from parallel to serial, the disc drives are able to transmit data from point to point, instead of sharing bandwidth across a single common data bus. Therefore, SAS virtually eliminates the bottleneck that parallel SCSI processing could never overcome.

John Monroe at Gartner indicates, "SAS is now being qualified by the major OEMs. By 2008 to 2010 (estimates vary) all SCSI drives will be SAS drives". Some IT OEM's have an even more aggressive rollout schedule. Referring to SAS disc drives, Craig Butler at IBM states, "The drives will become standard on servers by 2006". Although serial processing technology is new to enterprise servers, it is not new to the IT industry. Serial connections are commonly used on USB connections, on Fire Wire, and for almost all new printer connections. Enterprise servers are actually late in adopting the serial technology that can reduce bottlenecks and increase data processing speeds.

Most large IT server providers are currently launching products that take advantage of serial processing. Over the next year, almost all server manufacturers will launch servers that are built entirely on serial attached SCSI technology. Although you might not be able to see the difference from the outside, the storage inside of these new SAS servers will be faster and more reliable.


But SAS servers are not the end state for the advancement of data processing performance and reliability. A new smaller, faster, more reliable drive has already been introduced by Sun, IBM, and HP. This new small form factor 2.5" drive takes performance and reliability to the next level, surpassing even the larger 3.5" SAS drives. The small form factor (or SFF) drives also uses the serial technology interface, but delivers more capacity in gigabytes per U space and increases performance in Input/Output per Second per U space (1 U = 1.75" in a server rack cabinet). Not only does the IOPS per U space increase performance with SFF drives, but the maximum sequential data rate also goes up substantially.


Naturally, most IT providers recognize SFF SAS hard drive technology as the next step in meeting the performance and storage requirements for data hungry companies. Although SFF SAS drives have just started to appear on the market, by 2007 almost all server manufacturers will begin offering them as standard features on new servers.

Seagate is helping to drive this transition. "Seagate's Savvio enterprise-class 2.5-inch small form factor disc drive is the result of extensive research with HP and other leaders interested in solving end-user IT challenges to improve IOPS performance, consolidate space, and reduce power consumption," said Sherman Black, Seagate Senior Vice President and General Manager of Enterprise Storage. Reinforcing the 2.5" drive transition Dave Reinsel, director of storage research at IDC says, "Small form factor enterprise-class drives will equate to 60% of all drives integrated into internal storage environments by the end of 2009."

By combining Serial Attached SCSI technology and the small 2.5" drive form factor, data centers will see a huge boost in IOPS per U. As perpendicular drive technology advances, customers will also see an increase in the amount of storage capacity in a single U space.

In addition to greater IOPS per U, SFF drives provide numerous other benefits to customers. The reliability of SFF drives is greater than larger drives. Industry drive manufacturers indicate 2.5" drives have up to 15% better mean time between failure results (higher reliability) than the large 3.5" drives. The increase in reliability is created primarily by the tighter drive packaging, smaller parts, and improved vibration attenuation. When handling transactional data, which must be available 24x7x365, increased disc drive reliability is important to enterprise customers. Data protection also gets a boost from small drives, thanks to the ability to deploy RAID 5 protection on 1U servers. Most servers will see an increase the number of drives from 50% to 100% when they adopt the small form factor. The smaller drives make it possible to populate a 1U server with 4 or 6 drives instead of just 2, and therefore deploy a solid RAID 5 configuration.

In addition to reliability, performance also increases dramatically on SFF drives, thanks to the smaller platter and consequently shorter seek times. A few independent benchmark tests have been conducted which substantiate the performance of SFF drives.

Naturally, rebuild times are also much quicker with small disk drives. The small drives allow data to be spread over more spindles, which allow for fast re-build. Flexibility is also improved for customers who will be able to mix and match different drives in the same back plane. A unique feature of the SAS technology allows both the high end Serial Attached SCSI and the entry level Serial ATA drives to be mixed and matched in the same serial drive cage. Customers might choose to have one JBOD with 5 SAS SFF drives on one RAID set running mission critical applications, while 5 SFF SATA drives are in the same JBOD storing reference data. Customers now have unprecedented flexibility and opportunity to lower their total cost of IT ownership by selecting the right hard disc drive for the proper application.

As power and cooling become bigger concerns in modern data centers, it is reassuring to know smaller drives consume less power and produce less heat. The new SFF SAS drives consume approximately half the power of the larger 3.5" drives of equivalent capacity. Additionally, smaller drives produce less noise than their larger counter parts, helping to create a more work friendly data center environment.

The industry transition period on the journey from parallel SCSI to SFF SAS hard disc drives will not take long. Once customers become aware of the value and advantages, they will begin requesting 2.5" SFF SAS drives. We can expect to see some server providers jump on the SFF SAS disc drive band wagon immediately, transitioning customers in one step. Other server providers will create a two step transition: first to large 3.5" SAS drives and a second transition to SFF 2.5" SAS. A two-step transition may incur greater costs for customers who have to qualify new server technology twice. Alternatively, server providers who make an immediate move to SFF SAS drives in a single step transition may be able to save their customers money by avoiding multiple qualification cycles. The end state seems clear: Small Form Factor 2.5" SAS disk drive technology will provide customers with the ultimate in performance and reliability for their IT server environments. Sooner or later all servers will have SFF SAS drives as standard equipment in their drive cages. The only question is which OEM server providers will transition their customers quickly and which ones will try to hold on to the less reliable, lower performing, power consuming, large form factor 3.5" hard disc drives?

Bob Moore is in the marketing organization at Hewlett Packard (Palo Alto, CA).
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Title Annotation:Storage Networking; Small Computer System Interface
Author:Moore, Bob
Publication:Computer Technology Review
Geographic Code:1USA
Date:Jan 1, 2006
Previous Article:Interactive exploration of non-indexed data.
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