分类： 服务器与存储
2008-03-04 09:37:07
Improvements continue in form factors, rotation speeds, interfaces,
recording technology, energy consumption, and encryption.
In an industry known for its cyclical up/downturns, the hard disk drive (HDD)
market appears to be relatively stable. The TrendFocus market research firm
expects HDD shipments to surge from 495 million in 2007 to 768 million in 2011,
a compound annual growth rate of 11.61%. However, in a testament to the ongoing
decrease in cost-per-gigabyte, HDD revenues are expected to grow from $31.3
billion in 2007 to $33.3 billion in 2011, a CAGR of only 1.56% (see figure,
below).
For 2008, another market research firm-International Data Corp. (IDC)-predicts a near-double-digit growth rate of 9.3% in terms of unit shipments, fueled largely by the mobile segment of the overall drive market.
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And in good news for the disk drive manufacturers that got battered in a
volatile 2007, Needham & Co. financial analysts predict that 2008 could be
the most profitable year ever for the HDD industry.
Most disk drives come in either a 3.5-inch or 2.5-inch form factor. Whereas the 3.5-inch form factor has been the workhorse of the enterprise segment of the market (i.e., non-desktop/portable), the industry is migrating to the 2.5-inch form factor, which was previously relegated primarily to the laptop market segment.
“In the server space, the 2.5-in form factor is in use industry-wide,” says Marty Czekalski, senior manager of market development at Seagate Technology,
When you consider “speeds and feeds” in HDD technology, the pacing features are transfer rate and rotational speeds. In the enterprise segment of the market, rotational speeds are typically 10,000rpm or 15,000rpm for both 3.5-inch and 2.5-inch drives. How- ever, Hossein Moghadan, Western Digital’s CTO, notes that those rotational rates apply mainly to online, or primary, storage applications and that 7,200rpm drives are common in nearline, or secondary, applications.
Transfer rates generally scale with the rotational speed. However, Richard New, director of research at Hitachi Global Storage Technologies (GST), points out that there are two aspects to consider when you are examining transfer rates: the peak transfer rate, which is proportional to rotational speed and linear density, and the random access rate, which is driven by seek time and rotational latency.
Ultra-high-speed HDDs rotating at speeds exceeding 20,000rpm have been demonstrated in manufacturers’ labs, but they have not been commercialized due to heat generation, power consumption, noise, vibration, and other problems that generally suggest a lack of long-term reliability.
The venerable parallel SCSI interface is nearing its end of life. In an InfoStor reader poll, only 4% of the respondents said that parallel SCSI will be their primary drive interface over the next 12 months (see figure below).
But the heir apparent to parallel SCSI is still unclear. In that same InfoStor reader survey, 35% of the respondents cited Fibre Channel as their primary drive interface over the next 12 months, while 32% cited SATA and 29% said that SAS would be their primary interface.
IDC predicts that this year SATA will account for almost 40% of all
enterprise-level disk drive shipments, followed by Fibre Channel at about 24%
and SAS at 23% (see figure on p. 26). Somewhat surprisingly, IDC expects
parallel SCSI to account for 12.7% of enterprise HDD shipments this year.
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Gartner Dataquest’s predictions are somewhat different. In 2008, Gartner
expects SAS to account for about 41% of multi-user HDD shipments, followed by
SATA at 29% and Fibre Channel at approximately 23% (see figure below). Parallel
SCSI is expected to have only a 7.3% market share.
Improvements in read/write head technology and media technology are expected to match an expected 40% improvement in areal density over the next year. Many of the changes in heads and media technology took place over the last year or so as perpendicular magnetic recording (PMR) displaced traditional longitudinal recording. Perpendicular recording, which was introduced on 3.5-inch drives in mid-2006, is believed to be capable of delivering up to 10x the storage density of longitudinal recording on the same media.
“Perpendicular recording is here to stay,” says Dr. William Cain, vice president of technology at Western Digital. “The whole industry has switched to perpendicular recording over the last year.”
Perpendicular recording overcomes the constraints imposed by the “superparamagnetic effect,” which occurs when the microscopic magnetic grains on the disk become so tiny that ambient temperature can reverse their magnetic orientations, causing data loss.
In longitudinal recording, the magnetic orientation of the data bits is horizontal, or parallel, to the surface of the disk. In perpendicular recording, the magnetic orientation of the data bits is aligned vertically, or perpendicular, to the disk. With perpendicular recording, it’s harder to reverse the magnetic orientation of the bits.
Perpendicular recording has spurred further research into head and media technology. For example, Hitachi GST claims to have developed the world’s smallest read head for HDDs, which is expected to quadruple current drive capacity to 4TB on desktop drives and 1TB on notebook drives. But the heads-dubbed current perpendicular-to-the-plane giant magneto-resistive (CPP-GMR) heads-aren’t expected until at least 2009.
Disk drive manufacturers are doing their part in the overall effort toward more “green” data centers. For example, some manufacturers have introduced “power-down” drives (also sometimes referred to as “sleepy drives”), where the drive spins down when not in use. This can be advantageous in disk-based backup arrays, virtual tape libraries (VTLs), and other applications where files are accessed infrequently. When files on powered-down drives are needed, the array starts them spinning again.
Powered-down drives don’t need cooling, which reduces an array’s overall power consumption.
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Western Digital’s Moghadan cautions that a complete power down could draw too
much wattage upon spin up. With that in mind, WD offers IntelliPower technology,
which balances spin speed, transfer rate, and caching algorithms to avoid always
spinning at top speed. Also, less current is used during spin up, allowing more
drives to spin up simultaneously, which results in faster system readiness.
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Similarly, disk-array vendors such as Copan (which pioneered the concept) and
Nexsan have massive array of idle drives (MAID) technology, in which a
proportion of drives in an array are shut down to save power. In Copan’s
implementation, up to three-quarters of an array’s drives are powered down at
any given time. This results in much less heat generation; also, more drives can
be packed into an array. Fujitsu also offers MAID technology in its Eternus line
of disk arrays.
In an effort to address data security issues, HDD drive manufacturers are working on drive-level encryption.
Gianna DaGiau, senior marketing manager for Seagate’s Enterprise Compute Business unit, explains how the company’s Full Disk Encryption (FDE) technology works: “When you do a write, the cleartext enters the drive and, before it is written to the disk, it’s encrypted using an encryption key embedded in the drive. When the data is read, the encrypted data is deciphered before it leaves the drive.” Drive-level encryption is enabled by an ASIC on the drive that handles encryption
Seagate and other drive manufacturers already offer encryption on their desktop and notebook drives, but all vendors plan to add the option to their enterprise drives. Seagate, for example, plans to offer encryption on some of its enterprise drives later this year. The company claims that drive-level encryption will not negatively affect performance. As part of a deal announced at last fall’s Storage Networking World (SNW) conference, IBM announced that it will provide key management for Seagate’s encryption. LSI will also participate in the technology by developing controllers that work with the “self-encrypting” drives.
