The SSD Anthology: Understanding SSDs and New Drives from OCZ
by Anand Lal Shimpi on March 18, 2009 12:00 AM EST- Posted in
- Storage
Why You Should Want an SSD
For the past several months I’ve been calling SSDs the single most noticeable upgrade you can do to your computer. Whether desktop or laptop, stick a good SSD in there and you’ll notice the difference.
I’m always angered by the demos in any Steve Jobs keynote. Not because the demos themselves are somehow bad, but because Jobs always has a perfectly clean machine to run the demos on - and multiple machines at that. Anyone who has built a computer before knows the glory of a freshly installed system; everything just pops up on your screen. Applications, windows, everything - the system is just snappy.
Of course once you start installing more applications and have more things running in the background, your system stops being so snappy and you tend to just be thankful when it doesn’t crash.
A big part of the problem is that once you have more installed on your system, there are more applications sending read/write requests to your IO subsystem. While our CPUs and GPUs thrive on being fed massive amounts of data in parallel, our hard drives aren’t so appreciative of our multitasking demands. And this is where SSDs truly shine.
Before we go too far down the rabbit hole I want to share a few numbers with you.
This is Western Digital’s VelociRaptor. It’s a 300GB drive that spins its platters at 10,000RPM and is widely considered the world’s fastest consumer desktop hard drive.
The 300GB VelociRaptor costs about $0.77 per GB.
This is the Intel X25-M. The Conroe of the SSD world, the drive I reviewed last year. It costs about $4.29 per GB; that’s over 5x the VelociRaptor’s cost per GB.
The VelociRaptor is the dominant force in the consumer HDD industry and the X25-M is the svelte bullfighter of the SSD world.
Whenever anyone mentions a more affordable SSD you always get several detractors saying that you could easily buy 2 VelociRaptors for the same price. Allow me to show you one table that should change your opinion.
This is the Average Read Access test from Lavalys’ Everest Disk benchmark. The test simply writes a bunch of files at random places on the disk and measures how long it takes to access the files.
Measuring random access is very important because that’s what generally happens when you go to run an application while doing other things on your computer. It’s random access that feels the slowest on your machine.
| Random Read Latency in ms | |
| Intel X25-M | 0.11 ms |
| Western Digital VelociRaptor | 6.83 ms |
The world’s fastest consumer desktop hard drive, Western Digital’s 300GB VelociRaptor can access a random file somewhere on its platters in about 6.83ms; that’s pretty quick. Most hard drives will take closer to 8 or 9ms in this test. The Intel X25-M however? 0.11ms. The fastest SSDs can find the data you’re looking for in around 0.1ms. That’s an order of magnitude faster than the fastest hard drive on the market today.
The table is even more impressive when you realize that wherever the data is on your SSD, the read (and write) latency is the same. While HDDs are fastest when the data you want is in the vicinity of the read/write heads, all parts of a SSD are accessed the same way. If you want 4KB of data, regardless of where it is, you’ll get to it at the same speed from a SSD.
The table below looks at sequential read, sequential write and random write performance of these two kings of their respective castles. The speeds are in MB/s.
| Sequential Read (2MB Block) | Sequential Write (2MB Block) | Random Write (4KB Block) | |
| Intel X25-M | 230 MB/s | 71 MB/s | 23 MB/s |
| Western Digital VelociRaptor | 118 MB/s | 119 MB/s | 1.6 MB/s |
If you’re curious, these numbers are best case scenario for the VelociRaptor and worst case scenario for the X25-M (I’ll explain what that means later in the article). While the VelociRaptor is faster in the large block sequential writes look at the sequential read and random write performance. The X25-M destroys the VelociRaptor in sequential reads and is an order of magnitude greater in random write performance. If you’re curious, it’s the random write performance that you’re most likely to notice and that’s where a good SSD can really shine; you write 4KB files far more often than you do 2MB files while using your machine.
If the table above doesn’t convince you, let me share one more datapoint with you. Ever play World of Warcraft? What we’re looking at here is the amount of time it takes to get from the character selection screen into a realm with everything loaded. This is on a fully configured system with around 70GB of applications and data as well as real time anti-virus scanning going on in the background on every accessed file.
| WoW Enter Realm Time in Seconds | |
| Intel X25-M | 4.85 s |
| Western Digital VelociRaptor | 12.5 s |
The world’s fastest hard drive gets us into the game in 12.5 seconds. The Intel X25-M does it in under 5.
SSDs make Vista usable. It doesn’t matter how much background crunching the OS is doing, every application and game launches as if it were the only thing running on the machine. Everything launches quickly. Much faster than on a conventional hard drive. If you have the ability, try using your system with a SSD for a day then go back to your old hard drive; if that test doesn’t convince you, nothing will.
That’s just a small taste of why you’d want an SSD, now let’s get back to finding a good one.
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SunSetSupaNova - Wednesday, March 18, 2009 - link
Just wanted to say great job Anand on a great article, it took me a while to read it from start to finish but it was well worth it!FHDelux - Wednesday, March 18, 2009 - link
That was the best review i have read in a long time. I originally bought an OCZ Core drive when they first came out. It was the worst piece of garbage i had ever used. Newegg wouldn't let me send it back and OCZ support forums told me all sorts of junk to get me to fix it but it was just a poorly designed drive. I eventually ended up getting the egg to take it back for credit and i wrote OCZ off as a company blinded by the marketing department. I currently own an Intel SSD and its wonderfull, everytime i see OCZ statements saying their drive competes with the Intel drive i would laugh and think back to the OCZ techs telling me i need to update my bios, or i need to install vista service pack 1 before it would work right.I am thankful that you slapped that OCZ big wig around until they made a good product. All of us out there that wasted our time and money on Pre-vertex generation drives are greatfull to you and the whole industry should be kissing your butt right now.
One thing these companies need to learn is that marketing isn't the answer, creating solid products is. Hopefully OCZ has learned their lesson, and because of your article i will give them another chance.
THANK YOU!
kelstertx - Wednesday, March 18, 2009 - link
I didn't want to worry about eventual failure of the Flash chips of an SSD, and went with an SDRAM based Ramdrive from Acard. These drives have no latency of any kind, since they use SDRAM, and no lifespan of write cycles. I've been using mine for a couple of weeks now, and I like it a lot. I put Ubuntu on mine, and had 2G left for my small home folder. The standard HDD is my long-term storage for data files, music, etc. As SDRAM gets more affordable over time, I can add DIMMs and bump up the size.I know this review was about SSDs strictly, so an SDRAM drive doesn't technically fit, but it would have been interesting to see a 9010 or 9010b in there for comparison. It beat the Intel SSD in almost all the tests. http://techreport.com/articles.x/16255/1">http://techreport.com/articles.x/16255/1
7Enigma - Wednesday, March 18, 2009 - link
I've been eying these guys ever since the announced their first press release. Every time I always was drawn away by the constant need for power (4h max on battery scares the bejeezus out of me if I was to be gone on vacation during a storm), high power usage at all times, and high cost of entry (after factoring in all of the ram modules).I really dislike that article as well, since I think the bottlenecks were much less apparent with such a horribly slow cpu. The majority of that review's data is extremely compressed. I mean a P4, and 1 gig of memory; are you F'ing kidding me? This article was written in Jan of this year!? Why didn't they just use my old 486DX?
tirez321 - Wednesday, March 18, 2009 - link
What would a drive zeroing tool do to write performance, like if you used acronis privacy expert to zero only the "free space" regularly? Would it help write performance due to the drive not having to erase pages before writing?tirez321 - Wednesday, March 18, 2009 - link
I can kinda see that it wouldn't now.Because there would still be states there regardless.
But if you could inform the drive that it is deleted somehow, hmm.
strikeback03 - Wednesday, March 18, 2009 - link
The subjective experiences with stuttering are more important to me than most of the test numbers. Other tests I have found of the G.Skill Titan and similar have looked pretty good, but left out mention of stuttering in use.Too bad, as the 80GB Intel is too small and the ~$300 for a 120GB is about the most I am willing to pay. Maybe sometime this year the OCZ Vertex or similar will get there.
strikeback03 - Tuesday, March 24, 2009 - link
When I wrote that, the Newegg price for the 120GB Vertex was near $400. Now they have it for $339 with a $30 MIR. Now that's progress.kamikaz1k - Wednesday, March 18, 2009 - link
the latency times are switched...incase u wanted to kno.also, first post ^^ hallo!
GourdFreeMan - Wednesday, March 18, 2009 - link
It seems rather premature to assume the ATA TRIM command will significantly improve the SSD experience on the desktop. If you were to use TRIM to rewrite a nonempty physical block, you do not avoid the 2ms erase penalty when more data is written to that block later on and instead simply add the wear of another erase cycle. TRIM, then, is only useful for performance purposes when an entire 512 KiB physical block is free.A well designed operating system would have to keep track of both the physical and logical maps of used space on an SSD, and only issue TRIM when deletion of a logical cluster coincides with the freeing of an entire physical block. Issuing TRIMs at any other time would only hurt performance. This means the OS will have significantly fewer opportunities to issue TRIMs than you assume. Moreover, after significant usage the physical blocks will become fragmented and fewer and fewer TRIMs will be able to be issued.
TRIM works great as long as you only deal with large files, or batches of small files contiguously created and deleted with significant temporal locality. It would greatly aid SSDs in the "used" state Anand artificially creates in this article, but on a real system where months of web browsing, Windows updates and software installing/uninstalling have occurred the effect would be less striking.
TRIM could be mated with periodic internal (not filesystem) defragmentation to mitigate these issues, but that would significantly reduce the lifespan of the SSD...
It seems the real solution to the SSD performance problem would be to decrease the size of the physical block... ideally to 4 KiB, as that is the most common cluster size on modern filesystems. (This assumes, of course, that the erase, read and write latencies could be scaled down linearly.)