20 Questions on SSD: Things you’ll want to ask.
Question #4: How consistent is the performance of your SSD?
In the last few blogs of our 20 questions on SSD series, we looked at OEM qualification, endurance, and power loss protection. In this blog, we’ll look at a question that’s critical to performance in RAID sets and planning in your data center, “How consistent is the performance of your SSD?”
We’ve talked about SSDs in the past with analogies using cassette tapes, Peter Frampton, and my vintage Honda Civic… This time, we’ll use the 1981 Yamaha XJ550 Seca I started riding in the late 80s. Let’s just say it was well worn (+50k miles) when I bought it for a mere $250 in 1988. It was a sweet ride and great on gas, exciting as I was completely broke at the time. The point here is it was a great bike... although it did have a small problem with the starter. Sometimes the starter worked, sometimes it didn’t, sometimes my 119 pound self just had to push start it, and most of the time I parked at the top of a hill just in case.
I never knew whether or not the starter would behave which was terribly frustrating. I could have used a little consistency.. which brings me to my point about SSDs. Planning in the Enterprise data center requires components that perform consistently and SSDs are no exception.
So let’s start with a couple of graphs, these are from some testing we did internally at our lab in the NVM (Non-Volatile Memory) Solutions Group here at Intel. The 1st graph on the left (in blue) is an Intel SSD DC3500 Series drive performing a mixed 70/30 read/write workload with 4k blocks across the whole span of the drive at a queue depth of 4. We used Iometer and a recent Intel Xeon E5-2600 server to create this load on the SSD. You’ll notice that the performance over time averages between 20-22k IOPS consistently during the entire duration of the test series. Next let’s look at a really good drive of the same capacity as the Intel SSD DC S3500 Series from a top manufacturer on the right (in red).
This graph is the result of running the exact same workload in the exact same configuration as the Intel SSD. You’ll notice immediately that if you average out the IOPS of both the Intel SSD and this other SSD, the other SSD is a bit lower... but pretty close. You’ll also notice that the other SSD occasionally peaks at about 2x IOPS, but also dips to only 70% the IOPS we see from the Intel SSD. We’ve found this type of inconsistent performance behavior in many of the SSDs we’ve evaluated internally from other manufacturers.
Now take a look at the RAID 0 scaling tests we did with the same drives. We used RAID 0 for demonstration purposes as it requires the least amount of overhead from the RAID controller. Perfect linear scaling is shown in gray, good scaling from a consistent SSD is shown in blue, and poor scaling from an inconsistent SSD is shown in red. What we found here is that the worst element in a RAID set dictates the overall performance of the array in general. In other words, you really can't duplicate Shakespeare's work by running a tornado through a pile of random shredded documents.
Now let’s frame this in terms of the Enterprise data center. For example, I’m planning for a new SQL database (DB) deployment and I’m putting SSDs in a RAID 5 for my main database files and a RAID 10 for my log files. The question is, “Do I want to plan around a drive that delivers the same consistent performance regularly?” I know that Intel Data Center SSD is going to cost a little more than the competition. However, my alternative is to deal with inconsistent performance and the potential for application problems that would be difficult to troubleshoot and impossible to reproduce. It's akin to asking whether or not you want a guitar amplifier that “goes to 11”… as long as you’re OK with a volume knob that sticks at “7” on an unpredictable basis. And... unlike my erratic starter in that XJ550 Seca, I can’t exactly park my database at the top of a hill every time and give it the old run, jump, & bump. I know which SSD I’d prefer for my production environment.
Consistency in performance, much like OEM qualification, endurance, and power loss protection are critical to data center deployments and come built-in with every member of the Intel Data Center Family of SSDs. I’ll be back in a few weeks to talk about more SSD goodness in the 5th installment of our 20 questions blog, see you then…
Christian Black is a Datacenter Solutions Architect covering the HPC and Big Data space within Intel’s Non-Volatile Memory Solutions Group. He comes from a 23 year career in Enterprise IT.
Follow Chris on Twitter at @RekhunSSDs.