SSD followup

I wrote a couple of months ago how the Intel SSD's were the only ones on the market that seemed to be worth buying - all the cheaper ones were unusable due to having horrible random write performance, which is something you notice really quickly in real life as nasty pauses.

Sadly, almost none of the reviews seemed to ever catch on to that, as they were all looking at the (totally irrelevant) throughput numbers that basically don't matter in any real-life situation. Everybody just quoted the nice big marketing numbers, because finding the numbers that matter more to actual human perception (notably: average and maximum latency) was so much harder, and most disk benchmarks are crap and don't even give those numbers.

Which is why I was so happy to see this review at AnandTech. Half the numbers quoted are still the worthless ones (I guess you can't avoid quoting the industry standard benchmarks, even when they are horribly bad), but much of the actual discussion is about how unusable a drive is when it has maximum latencies in the hundreds of milliseconds.

Looks like people are catching on. And as the reviewers are catching on, so are the manufacturers. I still see too many reviews that gush over throughput numbers, but here's one that got it right, and apparently got a manufacturer to actually understand. Good job.

(And I still love my Intel SSD's , but Anand is certainly correct in pointing out that they aren't cheap. And it looks like "cheap" will no longer necessarily mean "sucks so bad that they are unusable" in the upcoming drives. Hallelujah)

.. so I got one of the new Intel SSD's

The kernel summit was two weeks ago, and at the end of that I got one of the new 80GB solid state disks from Intel. Since then, I've been wanting to talk to people about it because I'm so impressed with it, but at the same time I don't much like using the kernel mailing list as some kind of odd public publishing place that isn't really kernel-related, so since I'm testing this whole blogging thing, I might as well vent about it here.

That thing absolutely rocks.

I've been impressed by Intel before (Core 2), but they've had their share of total mistakes and idiotic screw-ups too (Itanic), but the things Intel tends to have done well are the things where they do incremental improvements. So it's a nice thing to be able to say that they can do new things very well too. And while I often tend to get early access to technology, seldom have I looked forward to it so much, and seldom have things lived up to my expectations so well.

In fact, I can't recall the last time that a new tech toy I got made such a dramatic difference in performance and just plain usability of a machine of mine.

So what's so special about that Intel SSD, you ask? Sure, it gets up to 250MB/s reads and 70MB/s writes, but fancy disk arrays can certainly do as well or better. Why am I not gushing about soem nice NAS box? I didn't even put the thing into a laptop, after all, it's actually in Tove's Mac Mini (running Linux, in case anybody was confused ;), so a RAID NAS box would certainly have been a lot bigger and probably have more features.

But no, forget about the throughput figures. Others can match - or at last come close - to the throughput, but what that Intel SSD does so well is random reads and writes. You can do small random accesses to it and still get great performance, and quite frankly, that's the whole point of not having some stupid mechanical latencies as far as I'm concerned.

And the sad part is that other SSD's generally absolutely suck when it comes to especially random write performance. And small random writes is what you get when you update various filesystem meta-data on any normal filesystem, so it really does matter. For example, a vendor who shall remain nameless has an SSD disk out there that they were also hawking at the Kernel Summit, and while they get fine throughput (something like 50+MB/s on big contiguous writes), they benchmark a pitiful 10 (yes, that's ten, as in "how many fingers do you have) small random writes per second. That is slower than a rotational disk.

In contrast, the Intel SSD does about 8,500 4kB random writes per second. Yeah, that's over eight thousand IOps on random write accesses with a relevant block size, rather than some silly and unrealistic contiguous write test. That's what I call solid-state media.

The whole thing just rocks. Everything performs well. You can put that disk in a machine, and suddenly you almost don't even need to care whether things were in your page cache or not. Firefox starts up pretty much as snappily in the cold-cache case as it does hot-cache. You can do package installation and big untars, and you don't even notice it, because your desktop doesn't get laggy or anything.

So here's the deal: right now, don't buy any other SSD than the Intel ones, because as far as I can tell, all the other ones are pretty much inferior to the much cheaper traditional disks, unless you never do any writes at all (and turn off 'atime', for that matter).

So people - ignore the manufacturer write throughput numbers. They don't mean squat. The fact that you may be able to push 50MB/s to the SSD is meaningless if that can only happen when you do big, aligned, writes.

If anybody knows of any reasonable SSDs that work as well as Intel's, let me know.