Little blooming marvels

Perp' recording and increased board real estate space means 2.5 inch disks can do more, much more.


Perpendicular recording is driving disk capacity up 50 percent. At the same time increased integration at the chip level means that disk drive control board space availability is increasing. Thus more features can be put into a disk drive, such as encryption or a cache of flash memory.

These two changes are making 2.5 inch drives (HDDs) more applicable to notebook computers and consumer electronic devices such as set top boxes (STBs) and personal video recorders (PVRs). Drive suppliers are reaping the benefits.

Western Digital is ramping up its 2.5 inch drive shipments and they are approaching equality with 3.5 inch in the CE market. In its Q1 FY 07 numbers, unit shipments were approximately 2.2 million 2.5-inch mobile hard drives and approximately 2.5 million 3.5 inch hard drives for utilization in personal and digital video recorders — both fast-growing, newer markets for the company.

Hitachi GST has also recorded impressive 2.5 inch drive numbers with year-on-year growth of 36 percent'

HGST and Seagate are both vertically-integrated drive manufacturers. Western Digital is not. However, unlike the situation in chip foundries where a technology jump from, say 90nm to 65nm feature size, entails a huge jump in fab costs, the technology jump in HDD manufacturing from the last step - GMR or giant magneto-resistive heads - to perpendicular recording did not mean a massive increase in costs.

This enables a firm like Western Digital, very skilled at managing supply lines and manufacturing ramp up, to compete effectively with vertically-integrated HGST and Seagate.

Feature additions

Hitachi GST is extending its 2.5-inch product line. The line currently tops out at 160GB for the 5,400 rpm drives and 100GB for the 7,200 rpm models.

It anticipates a 200GB 7,200 rpm drive in the first half of 2007 and a 250GB 5,400-rpm drive later in the year, both versions using the serial-attached SCSI (SAS) interface.. These increases are due to perpendicular recording technology.

However, there is space enough on the drive control boards to add additional features. HGST is aiming to introduce versions of both new drives with flash memory (so-called hybrid drives) which will be usable by Vista, Microsoft's forthcoming version of Windows.

The effect of hybrid drives is to speed response time when data is in the flash cache and reduce drive spin time. The obvious benefits of this will be to reduce start (boot) time and prolong battery life.

Another feature being planned is encryption. In this respect HGST will be matching Seagate.

A third planned feature is a drop sensor. Drop resistance on Hitachi's 2.5 inch drives is helped by the drive's parking of read-write heads off the disk surface, known as Ramp Unload/load.

All three features are aimed at notebook users mostly. Enterprise drive arrays will not use drive-level encryption. (See a Decru interview for more on this.)

Will there be a performance impact, slowing down I/O? Stephen Pereira, HGST director EMEA, said: "No, there won't be any noticeable performance impact. It will be so minimal users won't notice it. Our engineers don't see any effect on performance on the encryption side."

This contradicts what Decru's EMEA director said in the interview referred to above.

Drive manufacturers are constrained in what they can offer as features. For example, it is pointless offering better interaction with drive array controllers as manufacturers want to multi-source disks and prefer to continue with the current simple interface.

Enterprise drive array use

Another aspect of 2.5 inch hard drives is that you can put more of them into an enclosure than 3.5 inch drives. Granted you have less overall storage capacity but you have many more spindles and many more read-write heads which drives up the overall drive array I/O bandwidth and responsiveness.

This aspect of 2.5 inch drives is driving up their use in enterprise drive arrays. Stephen Pereira said: "2.5 inch 10K drives are already in the data centre. All the main array vendors have or adopting 2.5 inch drives."

I had supposed that they wouldn't make the transition from notebook/CE use to the data centre because of a perceived increase in power consumption. I was quite wrong.

Phil White of ECC Technologies, Inc. set me right: "The power consumed by an HDD is primarily consumed by spinning the disks and the inertia of a disk varies as the 4th power of radius so as you increase the diameter of the disks, the power increases exponentially. When you reduce the size of the disks, the power decreases exponentially and much faster than the capacity decreases so that the number of watts per gigabyte consumed by the smaller diameter disks is less than the number of watts per gigabyte consumed by the larger drives."

"Therefore, from a power standpoint, arrays of tiny drives are superior to larger diameter HDDs."

Perpendicular recording 3.5 inch roadmap

HGST will extend perpendicular recording across its 3.5 inch drives as well. It's likely that one of the first results will be a 750GB capacity product in 2007. By the end of that year a 1TB 3.5 inch drive should be ready.

HDD manufacturing prospects

Pereira can't see any new entrants to HDD manufacturing. The capital costs to enter the industry are massive: "It's far too capital-intensive. Our new China factory took 14 months from start to the first drive leaving it. We had to move to China because virtually every cent counts in the HDD market. Will there be new entrants? Probably not."

The move to 2.5 inch technology amongst HDD manufacturers is now widespread. Pereira said six manufacturers are in 2.5 inch technology now with four remaining only in 3.5 inch: "All vendors see (2.5 inch) as a fairly strategic part of the market."

At the rate of capacity increase mentioned above manufacturers are likely to be able to make half terabyte 2.5 inch drives in 2008. It's likely that we'll see even more tiering of performance and capacity inside drive arrays as vendors like EMC, Hitachi Data Systems, IBM and NetApp consider the possibilities. We might see a top performance tier of 2.5 inch 10K with a lower capacity-optimised tier of 3.5 inch 7200 rpm and all manner of variations in between.

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