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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 ASUS, Fujitsu, Samsung and Sandisk 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
  • Consumes 9W
  • 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 Lost 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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RE: What we need...
By KristopherKubicki on 11/16/2006 10:58:27 AM , Rating: 3
Due to wear leveling, all of the bits would fail at the same time.

If you continuously wrote 1MB to a 1GB stick, wear leveling would distribute the bits that are written so that every bit would be written to once before one bit is written twice.

If you wrote 1MB to a 1GB stick every second, with 10,000 writes per bit before burnout, you would be able to write for about 1,000 * 10,000 seconds, or 115 days continuously. Obviously if you're using higher quality SLC media, that figure goes up by a factor of 10.


RE: What we need...
By Aikouka on 11/16/2006 12:22:55 PM , Rating: 2
Not necessarily, your reasoning is flawed in that it assumes that no data will ever remain the same or you could say it looks at free space only. I look at these SSD's and think "Operating System". Operating System files do see a decent amount of read access, but they don't tend to change too often (save viruses and such ;)).

Looking at it this way, you'll see that a lot of files may end up "blocking" the wear leveling algorithm and only allowing it to use a certain amount of space. Therefore, there's less time until these bits would be used over again and you'd begin to see more bits fail depending on how much space is available.

Here's a little ASCII diagram:


This is very small in comparison (obviously) to a real SSD, but it shows how the first group has only ever been written once and never changed, but this causes the later section to become the more volatile part. At this rate, you'd possibly end up losing 25-50% of your drive at some point. Of course I don't expect a system file to never be altered, but I'd expect it to be altered significantly less than say... the contents of your Temporary Internet Files folder.

There is no real method around this blocking issue unless you rewrite the bits that're being "blocked" to the same value, but why would you create an algorithm to cause the drive to last a shorter duration just for uniformity?

RE: What we need...
By zsouthboy on 11/16/2006 2:17:25 PM , Rating: 3
Just because the data doesn't change doesn't mean the memory can't move it around at will.

Enough with the FUD for flash, everyone (not picking on you).

Hilarious that people are worried about reliability of their data; we are all using hard drives right now, right? Do you *know* how many times your drive has gone, "Eh, this data has had to been corrected a few times. I'll mark it off, and move the data elsewhere."? Because that is what's happening, right now, transparently.

RE: What we need...
By Aikouka on 11/17/2006 1:16:24 AM , Rating: 1
Already thought of that, and then I realized this:

Why the hell would an algorithm be programmed to waste more of the lifetime (i.e. unnecessarily moving a file to another location just to even out the lifespan)? That's just stupid, illogical and wasteful.

RE: What we need...
By mindless1 on 11/24/2006 3:37:09 AM , Rating: 2
yes, it certainly does mean it can't move it around, beacause that would halve the performance.

"I f***ing cannot play Halo 2 multiplayer. I cannot do it." -- Bungie Technical Lead Chris Butcher
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