Solid-state Drives Ready for Prime Time
November 15, 2006 3:45 PM
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The OS and application data are continually becoming easier to fit on today's platters - why not move it to NAND? - Image courtesy Samsung
Do you need a solid-state drive? Samsung says you do, and here's why
DailyTech recently had the opportunity to sit down with Don Barnetson, Samsung's director of flash marketing, to chat about the future of NAND devices. Specifically, we picked Barnetson's brain about solid-state drives and future NAND storage.
Over the past few months, we've seen dozens of announcements about solid-state hard drives. PQI has
already announced a 64GB flash drive
(which coincidentally, is based on Samsung NAND), which
have all announced products based on solid-state hard drives. Given the fact that the hard drive has been the bottleneck on PC performance for years, the question has to be asked is solid-state technology ready to take us out of the dark ages of storage?
In the 90s, the largest advocate of more storage was Microsoft. The company insisted we have larger hard drives for Windows 95, then Windows 98. Then the next largest proponent for more storage became the application designers, pleading users to get larger hard drives for image manipulation or games. But today, I can fit Vista, Outlook (and all of those 2GB PST files) and even a few games in less than 1/10th of my 250GB hard drive. The other 100-odd gigabytes is mainly composed of MP3s and a few DVD rips. I am the prime candidate for a solid-state hard drive.
Most business users claim only a fraction of the hard drive space provided for them, especially considering most unique data gets written to a network anyway. The operating system and applications can all fit in less than 10GB of space, which is well within the sizes of solid-state hard drives today. Barnetson's group has calculated that during an 8-hour day the average hard drive:
Has about a 1% chance of failure per year
Loses about 7 to 15 minutes per day in productivity
The fact that we lose so much time alone due to hard drive spin-ups and seeks is alone appalling, but the decreased power consumption is what is driving solid-state adoption today. A NAND device uses less than 200 milliwatts during read/writes, and 0 watts when not being accessed. On the desktop this is relatively unimportant, but on a notebook the hard drive accounts for 10% of the total power draw. Cutting this number down to less than 1% means an extra 12 minutes of usage on my 2 hour battery.
When asked about the reliability of NAND-based hard drives, Barnetson had no problem shrugging off fears of write corruption of failure. "Samsung's solid-state devices have a MTBF of approximately 1 to 2 million hours." Typical disk-based hard drives have a mean-time between failures of approximately 100,000 to 200,000 hours. Since there are no moving parts, the only real point of failure is for something to come unsoldered or a problem with the physical bit during a write.
Obviously, write-errors are a huge concern for those who have used flash products in the past. Only a few years ago the highest-end flash media was only useable for 1,000 or so writes. At that point the physical bits would "burnout" and could no longer be flipped. Today's single-level cell (SLC, memory that stores one bit per cell) is rated in excess of 100,000 writes before burnout. Multi-level cell flash, memory that stores multiple bits per cell, is significantly cheaper but even then is still rated at over 10,000 writes before burnout.
Is 10,000 writes enough? Absolutely, assures Barnetson. Samsung memory uses a technique called "wear leveling" to distribute the writes on a media through as many groups of cells as possible. The idea behind wear leveling is that all of the cells have approximately the same amount of writes to them, maximizing the life of the device. Consider a typical computer that writes 120 megabytes per hour to the hard drive. On a 32GB solid-state NAND drive, wear leveling would distribute this data over the entire drive -- it would take 267 hours to fill the device once. Even on a multi-cell flash device, at this rate it would take no less than 150 years to burnout all the bits on the SSD. Single-cell drives are capable of ten times as many writes.
Even so, Samsung's initial solid-state drives are
all single-cell designs
. This first generation of SSDs are prohibitively expensive for most, but Samsung's SSD roadmap already has plans for multi-cell level drives as early as next year, which should bring the cost down considerably. Additionally, Samsung anticipates announcing drives in capacities of up to 128GB in early 2008.
Solid-state memory will not entirely replace disk drives. The fact is, media is more and more prevalent each day. 5 years ago, a fringe enthusiast may have had as much as 1GB of MP3s on his hard drive. Today even the average user may have 100GB of just
episodes on their hard drive. As an intermediate step hybrid hard drive, hard drives with multi-gigabyte NAND caches, will provide the 2007 stopgap before really big SSDs get cheap. These drives can load the entire operating system, some applications and even a little bit of user data (like Outlook PST files) onto the NAND.
Our insatiable appetite for media cannot be even remotely matched with the production of NAND memory right now, but for games and operating systems, solid-state devices are here and ready to go.
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New Math & Defrag
11/22/2006 1:39:19 AM
The key to getting this wear-leveling to work well enough to not exceed the expected write life of the cells is to spend several times as much on your SSD so you have mostly free space. If you have a 36GB drive and have it 30GB full, obviously the leveling can only occur on the remaining 6GB.
It cannot be a true wear-leveling that writes to each the same # of times, it would have to keep track of all writes to do this since a filesystem is dynamic in which data is retained- we aren't wiping the drive and starting over clean when actually using it. I'll ignore this factor though as I don't have the ability to do an equation that would approximate the toll it might take- and of course it would vary per use, user, data, etc - too many variables.
Some power users can easily write 512MB/hr. so the remaining space had one cycle _minimum_ in 12 hours.
NOW, if it takes 150 years to burn out all the cells at 267 hours per fill but we're filling the remaining space in 12 hours, let's do the math.
267 / 12 = 22.25
150 years / 22.25 = 6.67 years (to burn out ALL those).
To those dismissing defragmenting their SSD, we have a reason! That reason is so the wear-leveling can write to these lesser used cells too, instead of constantly to the other ones that were free. Even defragmenting, since it isn't a perfect wear-leveling, some of the files will be re-written onto areas that formerly had static files, so the new free space will still have some well exercised cells. You'll have to defrag more often to significantly change the odds there.
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