24 SSD DC S3700s: So Choice. If You Have The Means...
Modern SATA drives are already bumping up against the 6 Gb/s SATA interface's limits. For now, there's little way around that, though the horizon is filled with fast new interfaces and form factors. Today, circumventing the SATA performance ceiling somewhat defeats the purpose of client storage, and is entirely incompatible with the the SSD DC S3700's mission. It's all about giving buyers the right mix of affordability, flexibility, and features in a SATA-based drive.
Of course, affordability is in the eye of the beholder. But the SSD DC S3700 was designed for organizations looking for a cost-effective repository for large deployments. Intel's older client drives are being used in datacenters of all sizes, and the DC S3700 is aimed at the folks making buying decisions in those environments. It gives buyers more capacity and form options at a price similar to where the 3 Gb/s SSD 320 family debuted.
Naturally, building an almost-18 TB array with 800 GB SSDs isn't cheap. Each drive sells for $2,000 online. Want your own beastly array? Be ready to spend close to $50,000 for the privilege (and that's before the price of a suitably-fast server). Sure, you're spending a pretty penny. But relative to what similar capacity and performance would have cost previously, the SSD DC S3700 clearly benefits from faster, more economical MLC NAND manufactured using a high-yield 25 nm process.
Just because these drives aren't cheap doesn't mean we can't have fun with them. Without question, we can extract superb performance from just a few of Intel's SSDs. Scale up to 24, and you're talking about some serious speed.
All of this could have gone horribly pear-shaped without a proper server to drop the disks in. For what we wanted to do, we needed all of the performance our Xeon E5s could give us. We successfully found the limit of what the SSDs and our test platform could do together, and the result was on the (very) high side. The RAID 0 calculations performed by the host are fairly lightweight, but creating enough of a workload to stress the storage subsystem is fairly taxing.
The rewards really are worth the effort. We were able to turn those 17,880 GiB into a single high-performance volume capable of heroic performance. Getting to 1,000,000 4 KB read IOPS is nice, but witnessing almost 1,000,000 write IOPS is even better. Sequential performance is huge all-around. Software RAID has never been so nice.
And that might be the biggest surprise of all. If we were stuck benchmarking software RAID under Windows, we would have been stuck at a tiny fraction of the performance seen using mdadm. At the very least, this is a topic worth further exploration. Faster hardware and open source development have created a software RAID solution that might be a viable alternative to hardware in many situations. Because mdadm's options are numerous, and there isn't much documentation of user experiences when it comes to SSD arrays, it's entirely possible that further tweaking could yield even better results. Sadly, our time with the SSD DC S3700s was all too brief, and there are so many unexplored areas to tackle. That's going to have to be a story for another day though, because Intel already received our little care package back.
