Storage in Mobile: Flash vs. Hard Drives

Storage in Mobile: Flash vs. Hard Drives
by J. Gerry Purdy, Ph.D., VP & Chief Analyst, Mobile & Wireless, Frost & Sullivan:

        

I used to think that hard disk drive (HDD) and flash storage capacity for mobile was growing so fast that we’d soon have much more capacity than users would ever need. I don’t think that way any longer. Now, it appears that users will consume just about all the storage that can be cost effectively created. Here’s why.        

In the HDD area, companies like Seagate and Toshiba have been increasing the capacity of 1.8" and 2.5" mobile drives at the rate of around 40% per year. The average or sweet spot of HDD in full function notebooks in 2009 is 320GB. That will grow to be 500GB by 2010 (it’s already available in some high models today). And, HDD sweet spot capacity will grow to around 750GB in 2011 and 1TB by 2012 with the high end around 40% larger.
            
How much storage do users need anyway? While every user varies, it’s possible to at least make some educated estimates based on different types of data and the needs each user has for that data type. Here’s a rough estimate of the low and high side storage requirements in a notebook PC based on estimates of different size files and the number of each type. Here’s what the profile looks like and then a projection for five years:
            
 
Hard Disk Requirements (Notebook PC)

            

Since most notebook PDs have 320G of storage today, it covers most users needs quite well, but when you consider the growing use of digital photos and video, the user will have to upgrade to a notebook with more capacity within five years.
            
HDDs have great transfer rates but have some latency when accessing random locations on the disk. This is due to the disk having to rotate to the right location and then moving the disk head to the right track in order to then transfer to or write from the disk. So, over the years, disk drive manufacturers have been speeding up the rpm of the disk in order to reduce the time it takes to find random locations of information on the disk. But, drive manufacturers have found that they can’t spin the disk too fast because they would then consume too much power which, in turn, reduces battery life. As a result, most disks today run at 5400 or 7200 rpm.

Newer disk drives have higher bit density on each disk platter and, therefore, the drive can transfer more bytes per second for the same rotational speed. Think of it as a tractor picking up more marbles in a single scoop if the marbles are smaller. The latest disk drives have a radial density of 200 Gigabits per square inch and can transfer at the rate of 3 GB per second (Seagate Momentus 7200.4 at 500GB capacity and 7200 rpm).
           
Disk drives have incorporated a front side cache‚ using non-volatile memory to hold information being written to disk which, in turn, reduces latency of the drive. Information is quickly stored in the cache so the system can proceed to do other things. The cache can then write to the hard disk. Flash has been added to assist in reading information faster: you can read faster from Flash because it’s direct access‚ without any latency. The most often accessed information is placed on the flash area of the hybrid drives.

In the SmartPhone area where all storage is flash, Apple now offers 32GB in the iPod Touch and 16GB in the iPhone (Apple still offers a 120GB HDD based iPod). It’s likely that the capacity will double in the next year as the next generation of iPod iTouch and iPhone products are introduced. Here’s what the storage profile of an iPhone (or equivalent SmartPhone) looks like plus a similar projection for five years:

            
Flash Storage Requirements (iPod Touch, iPhone class)

In these flash based SmartPhone devices, 16GB appears to provide enough capacity for the low side typical user but not enough for the high side power user. And, in five years, most typical users will need over 50GB which appears to be reasonable. Amazing that we’d see over 100GB in an iPhone within five years but it looks to be quite reasonable based on the strides that SanDisk and Toshiba are making in the growth of capacity of flash due to Moore’s Law and multi-level cells that can store more than one bit in each flash cell.

Most mobile devices now include a microSD slot (except for Apple). SanDisk is the leading supplier of flash storage at retail with 16GB capacity available today. Customers typically buy the most flash storage available for a price point they can tolerate, often under $50. We’ll soon see microSD cards available in a 32GB capacity available in retail for under $100.

As in the past, we recommended all users back up their data on an external hard drive as well as backing up the critical files on a remote service in the cloud. There’s plenty of capacity available. The challenge is to make the best use of the storage and treat it as a valuable resource.