RRAM...

Crossbar says it can put a terabyte of nonvolatile Resistive Random Access Memory (RRAM) on a single small chip.  Access times are 20 times faster than flash.  The structure of the chip is three dimensional, meaning that the storage capacity is proportional to the volume of the chip, not the area (as is true for conventional DRAM or flash memory).  This offers the potential of fully electronic nonvolatile RAM with capacities equaling or exceeding those of rotating magnetic memory.

Hard disks and tape are gonna die.  The only question is when...

Memory Lane...

I remember this ad, which ran in one of the computer hobbyist magazines in the late '70s (probably Byte).  I remember thinking how amazingly inexpensive that system was.  Just a couple of years prior, I had purchased a used, broken Memorex 630 for $10,000.  I spent a month or so troubleshooting and fixing that thing, and ended up with a washing-machine sized 10 MB hard disk (5MB fixed, 5MB removable).  I had to build a computer to interface with it.

And IMSAI was selling a complete system with a miniature “Winchester” hard disk for just $6,000.  Cheap!

Magnetic Memory Breakthrough...

Those geeks of a certain age may remember magnetic bubble memories, which stored data in tiny magnetic domains stored on thin magnetic films.  Flash memory completely overwhelmed it, partly because of the much lower energy requirements (which translates into much higher density) of flash.  Now scientists at MIT has made a surprising advance that might just bring back the bubbles: they've figured out how to reduce the energy required to form and move magnetic bubbles by a factor of at least 10,000. 

This will likely have an impact in other areas as well, including magnetic disk storage (“hard disks”) and magnetic tape storage.  It isn't clear to me that this discovery will also result in an areal density improvement, something the storage industry is always looking for...

Apparent Multi-Disk Failures...

Seven or eight years ago I worked for FutureTrade (a now-defunct electronic stock and options trading company).  I was their CTO, and our datacenter (our very own, not a co-lo) was one of my responsibilities.  The 300+ servers in that datacenter actually executed our electronic trades, so there was a lot of money riding on their proper functioning.

Most of the servers used disk only for booting and logging, and these just used locally attached disks in a mirror configuration.  Our database servers, however, had fairly large storage requirements for the day (several hundred GB) and their performance was disk-bound.  So those servers used attached RAID5 subsystems. 

One fine day fairly early in my tenure there, we had a disk failure in one of those arrays.  This failure was picked up by monitoring software, and we scheduled a replacement/rebuild (a standard RAID5 activity) for that evening, after trading hours.  When we ran the rebuild, though, we got non-recoverable errors across a total of three drives (including the one that originally failed).  WTF?  Three drives failing simultaneously?  This is so unlikely as to be dismissible, which I did.  There had to be another explanation. 

One possibility was that the RAID controller itself (or its power supply) had failed, not the drives.  So we swapped the drives into another controller - same three drives reported bad.

Another possibility was that two of the three disks had actually failed some time ago, and we never noticed – and that turned out to be the real situation.  It turns out that if bad blocks exist on rarely read sections of the disk, the RAID controller won't know about these problems until the next time the entire disk is scanned – which is something that happens during a rebuild operation, of course.  Bingo.

So we then set up a periodic disk scan on all our RAID5 systems (we had 6 of them).  To our surprise, on the first such scan all 5 of the RAID5 systems that had not failed had bad blocks on disks – bad blocks that would have caused a rebuild operation to fail.  We ended up replacing all the disks in all six of our RAID5 systems, replacing the old consumer-grade disks with enterprise-quality disks (and paying a pretty penny for them!), and then doing the full-disk scans on a weekly schedule.  That ended our multi-disk failures, but it was a bunch of work to maintain.

This post triggered my memory of this incident; the author does a fine job of explaining how these apparent multi-disk failures can occur...

Solid-State Memory Breakthrough...

The news on solid-state mass storage just keeps getting better and better.  The latest: voltage-switched magnetoresistive memory, much more dense and much lower power.

Old-fashioned magnetic memory (tape and disk) is doomed – the only question is exactly how long it will take.  I'm pretty sure I'll easily live long enough to see this...

Disk Storage Density...

It just keeps going up, despite the never-ending warnings that “We're near the end of density growth!”

I just don't believe them any more.  I'm ready to believe that scientists will somehow find a way to read and write multiple bits on a single electron...

Just When an Old Storage Guy Thinks Tape Has Finally Died...

...like some sort of digital zombie, it rears it's bloody head again...

Is There Nothing That Amazon Can't Do?

Amazon Glacier: archival storage at about a penny per gigabyte per month, with a stated 11 9s durability/year.  Awesome.  I gotta get me some of that!

Organic Data Storage...

Researchers at Harvard University have stored an entire book (more than 5 megabits of data) in artificial DNA – and read the book back out.  This storage technique has very high density, and (at least theoretically) archival storage time measured in centuries or even millenia.  There is one small drawback at the moment: read/write times are on the order of days.  They'll need to speed that up by a few orders of magnitude before we can write off rotating magnetic storage and flash memory storage...

Holy Areal Density, Batman!

In the hard disk business, the way to get more data capacity is to increase the number of bits you can store on a given piece of disk surface.  This is called “areal density”, and it's usually measured in bits per square inch.  Areal densities have been improving at a fairly steady rate ever since the '70s, and the density march continues.  Seagate has just demonstrated 1,000,000,000,000 bits per square inch (a terabit/sq. in.), and promises 60 TB (terabyte) disk drives as a result.  Wow!

All Records for Bit Storage Size Smashed...

Down to a mere 12 atoms.  That does actually seem like we're approach a limit of sorts – it's hard to imagine that we can figure out how to write data on the side of an electron.  But perhaps I shouldn't be so pessimistic...

Hard Disk Cost...

To myself and a few of my friends, the chart at right brings back a lot of memories.  We used to work for Stac (where the Stacker disk compression utility was developed).  In the early '90s, we noted the steep decline in the cost per megabyte of disk storage, and wondered what that meant to the future of disk compression.  We concluded that disk cost was trending toward free (quite rapidly!), and that when disks were free, the value of disk compression would approach zero.  Then we thought about the implications of “free” disk space, and what sort of software might leverage it.  We came up with the notion of backing up to disk (instead of the then-pervasive tape backup), and the idea of compressing the data from many computers through what is today called “de-duplication”.   Unfortunately for us, and for many reasons, we never figured out how to turn that idea into a lucrative business.

Here's something that looks very much like an updated version of the chart we created back in the early '90s:

Matt Komorowski is the fellow who put this data together.  He also calculated the regression equation (at right).  He pointed me to another trove of data on historical disk storage costs. 

Reading through all this stuff was a real trip down memory lane for me...

The SSDs are Coming...

...and it looks like they're going to be great!

Storage in the Cloud...

It's starting to happen, thanks to the conjunction of cheap bandwidth and cheap storage.  Here's a great example: back up your Mac to Amazon's S3 (their storage-in-the-cloud service)...

Hard Disk Sizes, Over Time...

I came across the graph at right while reading the Wikipedia article on hard disk drives (I'm a geek, what can I say).  Like many other aspects of computer technology, hard disk drives keep increasing in capability (in their case, capacity and to a lesser extent performance) and decreasing in price.  The declining price curve ($ per megabyte) I've long been familiar with, but this chart of capacity over time was fascinating (click to enlarge).

In rough terms, it looks like for the past thirty years, average disk capacities have increased quite steadily by about 60% per year.  This is quite close to the same factor by which the $ per megabyte declines, and jibes well with an observation many people have made: the price per disk drive is relatively invariant.  I'm not sure if that's just coincidence, or if it reflects market forces driving the capacity inversely to the $ per megabyte...

The End Is Near...

For hard disk drives, that is.

The original electronic computers of the late 1940s and early 1950s had hundreds and hundreds of moving parts. The systems I worked on while I was in the U.S. Navy had reduced this to dozens of moving parts – lots of mechanical switches, some relays, cooling blowers (powerful fans), and large hard disks (the size of washing machines) and tape drives (the size of refrigerators) each of which had dozens of motors, actuators, gears, dashpots, capstans, etc.

Once the electronics themselves moved from vacuum tubes to solid state (transistors and integrated circuits), by far the most likely thing to break in a computer was a moving part. In the 1970s, as a data systems tech in the Navy, I spent much of my life cleaning, repairing, lubricating, and adjusting things that moved. The only other common failure was high-voltage solid state electronics, which in those days was still in its infancy. Basically, the fewer moving parts something had, the more reliable it was.

These days, a modern PC generally only has two kinds of moving parts (not counting mouse and keyboard): fans and hard disk drives. Modern direct current fans are very reliable, but they do occasionally still break. Hard disk drives are notorious amongst IT professionals for being the most likely source of problems on a PC. But solid state disk drives have been (a) small, and (b) outrageously expensive.

That's changing, and very quickly. Toshiba is about to introduce a 512GB solid state disk drive – bigger than the hard disk installed on most PCs. It will be pricey – but not outrageously so, and (like all electronic devices) that price will come down rapidly as competitors come on line and production volumes ramp up.

The hard disk is about to become a museum display. I give it 5 years at most, and possibly as little as 2 years.

The only moving part left will be the fan – and as low power electronics get better and better (which they are), the need for these will taper off and eventually disappear altogether...

Bits and More Bits

I have spent a considerable part of my career working in the general area of digital storage, on software related to hard disks, digital tape systems, CD-ROMs, etc.. The computer industry calls this entire area of technology simply “storage", by which (generally) they mean non-volatile secondary storage. More informally, storage is all those places your computer more-or-less permanently saves its bits, whether or not the computer’s power is on.

Virtually all aspects of storage have changed dramatically in the 30 odd years of my career, but clearly the most significant changes have been in hard disks. In the late 1970s, I purchased the first hard disk I ever owned. It was a used Memorex 630, manufactured in the late 1960s; I paid $10,000 for it. This marvel was the size of a extra-large washing machine, and had just over 7MB of storage. That works out to 0.14 cents per bit — very cheap at the time. I spent hundreds of hours designing and building a controller to interface that disk to my Z80 CP/M system, for the sole purpose of speeding up my software development process. By today’s standards 7MB is laughably small, but in the late 1970s that system gave me (so far as I know) the biggest, baddest microcomputer-based development system in the world. At that time, “serious” software development for microcomputers was mainly being done on minicomputers, and part of the reason for that was the better storage found on the minis.

Just recently I had to run down to Fry’s Electronics to buy a hard disk as a repair part for one of my servers. The disk that broke down and needed replacement was 40GB — over 5,000 times the capacity of that old Memorex 630. And it wasn’t the size of a washing machine — it was more like the size of a paperback book. But Fry’s didn’t have any disk drives as small as 40GB! The smallest one I could buy was 120GB — but hey, it was only $89, so what the heck. The cost per bit on that disk drive was about 0.000000074 cents per bit — almost two million times cheaper than that used Memorex 630.

Hard disks keep getting cheaper and cheaper, especially in terms of price per bit of storage (because they keep getting bigger as well). Over the thirty years since I bought that Memorex 630, the price per bit for storage has dropped at a quite consistent rate, with storage each year costing about 60% of what it cost the year before. If you project forward ten more years, a 10TB (10,000GB) hard disk should cost about $42 — except you probably won’t be able to buy one that small!

But will hard disks still dominate in the future?

Hard disks currently have the advantage in price per bit, and they are reasonably fast. But the rate of advance in the speed of hard disks has not kept pace with the increase in speed for every other aspect of computer systems. The result of this divergence is that hard disks are today the major bottleneck in computer system performance. The fact that your PC takes a minute or so to boot is almost entirely due to the low speed (by comparison to the rest of your computer) of the hard disk. A modern computer can retrieve an arbitrary chunk of data (a word, it’s called) from its main memory (RAM) in about one billionth of a second — but to do the same thing from a hard disk takes several thousandths of a second, which sounds fast until you realize that’s millions of times longer than from main memory.

So hard disks are the bottleneck. What kind of storage is faster than a hard disk? Several, actually, but only one is currently a serious contender: FLASH memory (which comes in several technical variations). The price per bit today for FLASH memory is about 100 times higher than hard disks — but it is falling much faster. The price per bit may cross that of hard disks as early as five years from now, and almost certainly by ten years. And FLASH memory is superior in just about every performance category: it is much faster than hard disks, much smaller, uses less power, and has no moving parts. There’s one big difference with FLASH, though, that points to an area where hard disks may remain cheaper: the cost of making FLASH is essentially linearly related to its storage capacity. This is not true for hard disks — it costs very little more to add more bits to a hard disk, once you have paid for the basic mechanism.

Tom’s prediction (barring the introduction of some radical new technology): ten years from now, FLASH memory will dominate storage, with hard disks relegated to the particularly large, and probably tertiary, storage systems. Old-timer storage geeks like myself will recognize this as being parallel to the old paradigm of RAM-disk-tape, wherein RAM was used for primary storage, disk for secondary, and tape for tertiary. I think we’re going to see tape completely relegated to backup (actually that process is already well underway), with disk becoming the new tertiary media, and FLASH the new secondary. If I’m correct, that means production volumes of FLASH will go up (driving price per bit down even more). The opposite will be true with hard disks: volumes will go down, at least reducing the rate by which the price per bit drops.

Given the rate of innovation in the storage industry, it’s always possible that some new storage technology will pop up and displace both FLASH and disk. Possible, but not, I think, very likely. The history of storage has been mostly one of incremental advances, with fundamental new technologies coming along relatively rarely. In fact, nearly all the contenders for mass storage have actually been based on the same technology (magnetic storage): hard disks, tape, core memory, and even bubble memory, are all variants of magnetic storage technology. FLASH is the first semiconductor contender, with battery-backed DRAM another variant that might gain some traction. Those two fundamental technologies underlie every commercially significant storage technology for the last forty years. Of all the experimental technologies I’ve read about or heard of, the only one that seems particularly promising to me is three-dimensional optical storage (especially holographic, but also the non-holographic). The reason I find them promising is the extraordinary densities they could theoretically achieve. But these are very much laboratory curiousities at the moment, and I wouldn’t give them too much of a chance of emerging into high-volume production within ten years.

Bet on FLASH.