Get a Solid State Drive: Wait No Longer for SSD ROI
~ Solid state drives are fantastically fast, but still pretty pricey. Is there a business case for installing SSDs everywhere? Richi Jennings lists the pros, cons, and hidden gotchas...
[This is a retread of a feature article I wrote in September 2012, which has since disappeared from the Web. The data are probably a bit out of date today, but the conclusion is still valid.]
An SSD is a large flash memory drive, usually packaged as a drop-in replacement for a regular hard drive — in the same form factor and with the same interfaces.
SSDs are fast. Even the slowest SSD gives you far better real-world performance than does the fastest conventional hard drive: at least 100 times as fast — probably more. This translates not only into improved user productivity, but also into higher quality work.
More User Productivity, Fewer Errors
Imagine starting Windows in seconds, not minutes. Imagine if unpacking a .ZIP file in the background didn’t bring the rest of your PC to a crawl. Imagine never feeling the need to dropkick your PC for its inexplicable slowness.
You’ll see a vast performance improvement using an SSD in a desktop PC. It’s even more noticeable on a laptop or netbook, which use slower drives than their desktop counterparts.
Research by the University of Maryland and others show that a faster PC means reduced user frustration, which in turn causes users to make fewer mistakes. This has an inevitable effect on productivity.
www.cs.umd.edu/Library/TRs/CS-TR-4371/CS-TR-4371.pdf
ROI of an SSD
It’s easy to demonstrate a positive return on investing in an SSD. Let’s make three extremely cautious assumptions:
The working life of an SSD is at least three years — 700 working days.
Your SSD costs £100 to purchase and £100 to install — £200 total.
Your knowledge workers’ time is worth at least a fully-loaded* value of £50,000 per year — 50p per working minute.
Based on these assumptions, our SSD easily gives a positive return on investment over its lifetime, so long as it returns just one productive minute per day (700 × £0.50 > £200). We can make an even more compelling argument for specifying new PCs with SSDs when it comes time for a desktop hardware refresh.
* Fully-loaded is an accounting concept, made up of salary, benefits, and overheads; typically calculated as 150–200% of the actual salary.
Performance Counts in Large Amounts (it's a Competitive World)
The primary reason SSDs are fast is the overhead needed for accessing data: basically, there isn’t any.
Conventional drives with spinning magnetic platters first need to seek — to move their heads over the correct track on the platter — then wait for the correct sector to spin under the head. This access time is typically around one hundredth of a second (10 ms). SSDs have no moving parts, so their access time is essentially zero (though it’s usually quoted as 0.1 ms, to account for the overhead of the PC chipset and internal SSD gubbins).
But, as usual, manufacturers’ marketing numbers are mostly pointless. Like most competitive consumer goods, a complex comparison gets over-simplified into one or two numbers: sequential read and write speeds. Those are easy to compare, but the figures don’t tell you much in the real world. In the same way that a 10 megapixel camera might be better than one with 15 megapixels, an SSD claiming a read speed of 150 MB/s might be faster than another that offers 200 MB/s.
A typical enterprise PC doesn’t spend much of its time sequentially reading and writing large files (exceptions include users working with large Photoshop or digital video files). So, instead of sequential access, I suggest you focus on random access performance.
Windows 7 includes a useful command line benchmark: WINSAT.EXE. Good SSDs achieve at least 75 MB/s random reads and 4 MB/s random writes. Compare that with a modern, mid-range hard drive, which might achieve 5 MB/s reads and 0.5 MB/s writes. An appropriate command line to test random read speeds would be:
winsat disk –read –ran –ransize 4096 –drive c:
Caveat emptor: Each model of SSD usually comes in several capacities — for example, in sizes of 32, 64, 128, and 256 GB. Note that the smaller variants are usually a little slower than the larger ones. This is because the drives are arranged internally with several parallel lanes of connection between the controller and each flash memory chip. The smaller drives do not include some of the flash memory on the internal board, so they aren’t able to exploit as much parallel processing as their larger siblings.
SSD: Still Spendy Devices?
“But,” I hear you cry, “SSDs are really expensive.” Street prices for mid-range desktop SSDs have been falling recently; they're now significantly below the magic £1 per GB.
Compare that with around 5p for 3 TB drives. You could conclude that SSDs are far more expensive, but that would be missing the point; it says less about how expensive SSDs are, and more about how inexpensive the conventional drive has become.
Will SSDs continue to come down in price? Almost certainly: the reason is our old friend, Intel co-founder Gordon E. Moore: he of the eponymous law. (Moore’s Law forecasts that the density of integrated circuits doubles every two years, which usually translates into falling prices.)
The first generation of desktop SSDs were based on NAND flash memory chips with a feature size of 50 nm, or about two millionths of an inch. First generation drives cost considerably more than today’s SSDs, which use 34 nm and 25nm parts.
Beware of Disk Space Management
There are a choice of philosophies that people may adopt when migrating to SSDs:
Choose an SSD that’s big enough for your PC’s storage needs, or
choose a smaller SSD, big enough only for your operating system, programs, recent documents, etc.; pair it with a larger, conventional hard drive, on which you can store your less-performance-critical files.
Obviously option (1) is more expensive up-front. Also, even the largest, 500 GB SSDs may not be big enough for some users’ needs, although two or more SSDs can usually be used in combination. Many recent PCs have native hardware support for techniques such as RAID0 striping or spanning.
Option (2) is popular among the cash-poor-time-rich, enthusiast set, but think carefully: Is it a suitable choice for your enterprise desktop PC users? The problem of juggling space between the two drives could wipe out any productivity benefit gained by using it.
PCs will soon be available that treat an SSD as a cache for a conventional hard drive, thanks to new Intel chipsets that support this feature.
This could, of course, be a suitable opportunity to understand why your users need more than, say, 100 or 200 GB of files sitting on their company-issued PCs! Judicious rationalisation or the use of cloud storage may bring other benefits, besides the ability to use less expensive storage.
Hybrid Drives: Good Compromise or Waste of Time?
Ever since 2005, when Microsoft began to tout Windows Vista’s ReadyDrive technology, industry watchers have been excited by the prospect of conventional hard drives that contain additional flash memory, acting as a cache. In theory, this gives the best of both worlds: fast, SSD-like access to frequently-used data, but large, inexpensive storage capacity.
In practice however, all the hybrid drives that came to market in the last seven years proved disappointing. They’re undoubtedly better than a similar hard drive, but even the most recent models don’t offer the sort of productivity benefits of true SSDs. They contain a relatively small amount of flash memory, and only use it as a read cache — they don’t speed up writes.
Not recommended, but keep an eye on this idea. Its time may yet come.
SSDs and Enterprise Security
Organisations of all sizes tend to have different security priorities from consumer PC users, either because they care about confidential data, or are forced into regulatory compliance. Here are two security aspects of SSDs that aren’t often discussed:
Full disk encryption: Some SSDs now contain hardware that encrypts the stored data. They integrate with the pre-boot authentication BIOS extension in some PCs to authenticate the user before permitting access to the data. They typically use robust techniques such as 256-bit AES. Because the underlying flash memory chips contain encrypted data, forensic techniques that try to read the chips directly are practically impossible.
Secure erasure: Tools designed to securely wipe conventional hard drives don’t work with SSDs; they make too many assumptions about how the underlying hardware works. This was demonstrated by researchers at the University of California, San Diego. Some manufacturers now provide software tools to securely erase an SSD, which is important for hardware lifecycle management — i.e., at the end of a PC’s life.
Mythbusting
Whenever the conversation turns to SSDs, there’s usually one know-it-all who brings up a standard canard or two. As ever, there’s often a grain of truth behind the myths, but they’re myths just the same.
Here are my top four frequent misunderstandings about SSDs:
SSDs wear out: Because each flash memory cell can only cope with a limited number of write operations, manufacturers build in 5-10% of slack space, which can be used in two ways to prolong the life of the drive:
As a pool of space to use when a cell goes bad (conventional hard drives use a similar technique to “spare” bad sectors).
To even the wear across the drive: the controller also uses the slack space to evenly distribute the writes across the available flash cells; this is known as wear leveling.
So, unlike many USB flash keys and cards, SSDs do not suffer from hotspots. Recent data from an anonymous French PC store indicate that SSDs are just as reliable as the average hard drive. Manufacturers usually guarantee SSDs for three or five years of heavy use.
www.hardware.fr/articles/810-6/taux-pannes-composants.html
SSDs slow down: Early SSD designs only perform at their best when brand new; immature firmware caused a semi-permanent performance drop of around 25% after some use. This could only be fixed by a low-level format, which would reset the drive back to factory-fresh state (but erase all its data).
Current drives do not suffer this problem; because for example, the firmware uses idle time to optimise the storage layout. (As you’ll see, this myth is related to the next.)
SSDs don’t work with Windows XP or Mac OS: Windows 7 and Mac OS 10.6.6 include several updates to work better with SSDs. For example, supporting the TRIM extension to the ATA controller interface helps improve long-term performance, but is not necessary — again, because of idle-time optimisation. Similarly, installing older versions of Windows on an SSD requires a little extra partition alignment planning for optimum performance — planning that’s not required with Windows 7.
You need a new motherboard: Although some newer SSDs can take advantage of the SATA 6 Gb/s standard — aka “SATA 3.0” — most users see plenty of real-world performance benefit using the 3 Gb/s connections on their current PC hardware. Remember: the performance benefit for most users is because of random access time, not raw transfer speed. Even if your choice of SSD comes with a 6 Gb/s interface, it should be backwards-compatible with older PCs.
The real-world performance difference between conventional hard drives and SSDs can be frighteningly large. It’s the most effective upgrade you can make to a PC, new or old. Your users will thank you for it.