Solid State vs Conventional Hard Drive

[MeanSquare]

A lot of questions have been asked recently about Solid State Drives (SSDs) vs Standard Hard-Disk Drives (HDDs) lately, ranging from “Is the extra cost of an SSD worth it?” to “What kind of performance boost can you expect with an SSD?”. The following is an attempt to answer the bulk of those questions in one spot.

First, a little background information: In order for programs and data to be worked on by the computer, they need to be loaded into memory. While they’re not being worked on, you need a place to keep them so they’ll be available when you want to work on them again. Storage devices fill that need. In order to store data and programs in a way that the computer can locate them when it needs to work on/with them, disk drives are organized in the following way: An HDD has one or more physical “platens,” or plates of magnetic material (some are single-sided, many use both sides), each with a “head” which physically moves over the platen as it spins to read or write data. An SSD has none of this. Physically, it is a set of memory chips with a driver program that makes it appear to be the same as an HDD to the operating system. The first step in reading or writing data from an HDD is to make the drive "spin up" to a constant speed (4800rpm on the UX drives). This takes very little time, but it's time that an HDD has to take where an SDD doesn't.

The overall structure of an HDD (as well as floppy disks, CDs, and DVDs) is divided into Tracks and Sectors. The tracks are concentric rings spaced just far enough apart that the data written on one track won’t over-write the next one. These tracks are then divided into sectors, each of which holds a particular amount of data (almost always 512 bytes). When an HDD is formatted, these Tracks and Sectors are laid out on the magnetic media. The sectors are further organized into "clusters" of sectors which appear to the operating system as a single unit. Ideally, clusters are made up of sectors that are physically next to each other on the disk, but as disk space is used, more clusters will contain sectors that are physically apart from each other. In addition, files routinely take more than one cluster to store and those clusters may occupy different physical platens, tracks, and sectors. These are two forms of "fragmentation." Since it takes time for the head to move to a particular track and for the platen to rotate so a particular sector to rotate to a position where it can be written or read, the more fragmented a file gets, the more time it takes to read, write, or load it. Defragmentation software corrects this by physically moving the data in files so that it is located physically together on the disk. The best recommendation for keeping HDD performance at an acceptable level is to "defragment" the HDD regularly. There are even some utilities (Diskeeper, for example) which continuously defragment the HDD so it never gets defragmented very much.

On SSDs, there is no need for tracks or sectors. The underlying memory locations of the SSD are organized into clusters which the operating system can work with just as it does the clusters on an HDD. Since there are no physical sectors underlying the clusters on an SDD, files do not become fragmented on the sector level at all. Files can still be fragmented as the clusters occupy data locations that are physically apart from each other, but the effect of even that fragmentation has nowhere near the affect of cluster fragmentation on an HDD. It takes much less time for an SSD to electronically change the memory address to the next cluster in a file than it does for an HDD to move the heads and wait for the cluster's sectors to rotate under the head. You should hardly ever need to defragment an SSD. If it makes you feel better, you could do it once a month to eliminate cluster fragmentation, but you'll be hard put to notice any ill effects if you miss several months.

The hardware differences between HDDs and SSDs (read "no moving parts") give SSDs a number of advantages: First SSDs use less power and consequently generate less heat. How much less? Mechanical hard disks typically devour around 500mA while flash SSDs consume a mere 50mA. SSDs are also generally faster for the reasons stated in the preceding paragraphs. How much faster? Using FutureMarks PCMark5 benchmark program, measuring MB/second, we get the following results:

Test_________________HDD____SSD
Startup:_____________4.309__11.828
Application loading: ___3.196__11.697
General Use:_________2.528___8.551
Virus Scan: _________21.932__43.041
File Write: __________19.158__16.746

SSDs are many times faster in reading and mixed operations, but a tad slower on writes. SSDs are also completely unaffected by magnets. In addition HDDs require special hardware and firmware to quickly park the heads when the unit experiences sudden accelleration (such as dropping to the floor from your butter-fingered hand). Without these safeguards, the heads on the HDD will come into contact with the platen causing a dreaded "head crash" which usually breaks the head and renders the drive useless. SSDs are impervious to drops.

The pros aren't entirely in the SSD side of the chart, however. HDDs are available in much larger capacities than SSDs -- even those that fit into handtops. Currently, the largest SSD that fits into a handtop is 32GB. The largest handtop-compatible HDD is currently 100GB; over three times the capacity. In another year, we're likely to see 64GB SSDs in handtops, but we may well see 200GB HDDs as well.

SSDs also cost quite a bit more than HDDs, both in terms of cost per Gigabyte and in terms of overall cost. Going with a 32GB SSD instead of a 40GB HDD adds $400-$500 to the cost of a handtop.

There's one final factor in choosing an SSD or HDD. If you buy a UX with an HDD, you'll get the boring silver casing. If you buy one with an SSD, you get either the cool looking all black casing or the equally cool dark blue casing.

So is an SSD worth it? Only you can decide that. But now you have the information to make the choice knowledgeably.

[UXaficionado]

thanks for that comprehensive summary.

[Benz145]

Wonderful MeanSquare, I couldn't have asked for a better guide for people to understand the differences, and advantages/disadvantages of the different types of drives. I myself am now more knowledgeable when it comes to HDDs and SSDs! Very nice work, thank you for writing this!

According to your results of the SSD benchmark, since the numbers we see in a category like "startup" are more then double that of the standard HDD, can we expect the UX to startup twice as fast? Does the same go for the other categories?

One thing you might want to note - SSDs have a limited Write lifespan. That means once they have been written on so much, they pretty much die. Usually SSDs are rated according to how many times they can be written on, some last for a few years (maybe two), and others upwards of 5+ years. Those time frames are all based on average use of course, its all about how much you write to the drive. For this reason, Defragmenting an SSD is NOT RECOMMENDED. When the defragmentation occurs, it basically copies the data and moves its physical location from one area of the drive to another, during which it obviously needs to write that data into its new location. So as I said, frequent defragging of SSDs is not recommenced if you are looking for your SSD to have a long and healthy SSD life. MeanSquare mentioned above how defraging an SSD hardly effects performance anyway, so you shouldn't run into any problems dealing with not defragging your drive.

Quote from Wikipedia:

Shorter reliable lifetime - Flash based SSDs have relatively limited read/write cycles compared to hard drives which can last over a decade without mechanical malfunction. This is significant since in many systems, certain hard drive locations may regularly be accessed tens of thousands of times within even short periods. However, there are file systems developed especially for such purposes.

I'm no SSD pro, so please feel free to correct me if this info is incorrect : P

Also, if someone could ascertain the write life span of the UX's SSD, it would be much appreciated.

[ameen]

Originally Posted by MeanSquare

Currently, the largest SSD that fits into a handtop is 32GB...In another year, we're likely to see 64GB SSDs in handtops...

Thanks for sharing the information.

Please see this link for a 64GB SSD-drive announced to be released this year:

http://www.engadget.com/2007/03/27/s...uick-64gb-ssd/

[Floodguy]

MeanSquare,

thanks for the post. Did you wrote this on your UX ?

But still one questions is not answered yet: Can we exchange the UX's HDD with a SSD drive or not? Still no detailed information about the connector specs.

[sev7en]

Great tribute MeanSquare,
I missed the news about the defrag, I do usually that with my HDD but I'll leave away my SDD!

Just a question: the file writing test, it for a casual o linear write task?

[sev7en]

Originally Posted by Floodguy

MeanSquare,
But still one questions is not answered yet: Can we exchange the UX's HDD with a SSD drive or not? Still no detailed information about the connector specs.

Yes, you can. You need only a special adapter, I read about it in our forum: we already spoken about that... do a quick search, I'll do same for you

[Floodguy]

Originally Posted by sev7en

Yes, you can. You need only a special adapter, I read about it in our forum: we already spoken about that... do a quick search, I'll do same for you

Yes, I know.
But has someone actually done it with their UX?

[GETZO]

Thanks MeanSquare.

Very detailed information.

[MeanSquare]

To answer a couple of questions:
An SSD may not always be twice or even three times as fast as a conventional drive, but, when I put the two side by side in the same tasks, it is always noticeably quicker. I recently turned Aero Glass back on on my UX to see how it worked. (Admittedly, this is on a tweaked machine.) I didn't notice it slowing things down much at all so I've left it on (!)

As benz145 pointed out, it is not advisable to defrag an SSD regularly at all. Current SSDs have a block write capability of 100,000 times. That value is increasing. but it's still a finite number. However, "write endurance" is actually less of a problem than it could be. All manufacturers of SSDs currently embed management software into the firmware of the SSD. One aspect of this software is that it "scores" how many times a block of memory has been written to and then reallocates "over-written" blocks to different locations dynamically. Some manufacturers go even further. SiliconSystems has a patented algorithm which practically doubles the lifetime of an SSD over simple wear leveling. Adtron actually adds a bit of spare flash blocks to be used the case where a block will no longer be usable. All of this happens in firmware and is invisible to both the operating system and the end user and, since the firmware locks out blocks at the point where they would probably fail (instead of waiting for a failure), you never actually lose the data in those blocks. Also, since it is writing that causes the problem, even when a drive locks has no space left to store data due to block lockout, you can still copy the contents to a new, usable drive.