Why data center solid state drives (SSDs)!

Why choose a data center class SSD...

In my recent travels, I’ve had a number of questions from end users about the differences between data center series and client series Intel’s SSDs. Folks have expressed the desire to use the less expensive client drive, specifically the Intel SSD 530 Series client drive in place of the Intel SSD DC S3500 Series data center drive in a data center workload. What I’d like to convey is the reasoning for using a data center product, so we’ll do a little walkthrough in this blog. For this “why” exercise, we’ll use the specification sheets listed below and some estimated web pricing for the 80GB versions of these drives as a reference. We’re using the smallest common size of drive to highlight the differences between the two classes of device. At this lowest capacity point the GB/Day in write endurance is similar, which is normally what spawns this discussion.

Here are the specification sheets:

Intel SSD DC S3500 Series product specification: http://www.intel.com/content/www/us/en/solid-state-drives/ssd-dc-s3500-spec.html
Intel SSD 530 Series product specification: http://www.intel.com/content/dam/www/public/us/en/documents/product-specifications/ssd-530-sata-specification.pdf

For those new to the SSD space, write endurance is how long the device will last typically specified in GB/Day or TBW (terabytes written). Here are the endurance ratings from the specification sheets, and some roughly estimated web pricing.

Endurance rating 80GB Intel SSD DC S3500 Series: 45TBW for 80GB Drive – Estimated web pricing $120.00 (December ’13)
Endurance rating 80GB Intel SSD 530 Series: 20GB of host writes per day – Estimated web pricing $80.00 (December ’13)

Looking at the spec sheets closely you’ll notice that the TBW (terabytes written) increases with the capacity of the Intel SSD DC S3500 Series whereas all the 530 Series drive’s write capacity is fixed at 20GB/day. The write capacity of the client drive does not scale as the capacity of the drive increases.

Let’s start with endurance...

Evaluating the specification sheets, both drives are guaranteed for 5 years. For the 80GB Intel 530 Series drive, this guarantee is at 20GB host writes per day. For the 80GB Intel DC S3500 Series drive the specification lists 45TBW (terabytes written). Doing some quick base-ten math on the Intel SSD DC S3500 Series; 45TBW * 1000 gets us Gigabytes, then divide by 365 for years, and divide 5 for the number of years guaranteed gets us to almost 25GB of host writes per day for the 80GB Intel DC S3500 series drive. Then we cruise out to the web, pick a retailer or two, and come up with a roughly estimated holiday ’13 price for the 80GB Intel SSD DC S3500 Series at about $120.00 and the 80GB Intel SSD 530 Series at about $80.00.

At first glance, wait… 5 extra GB a day for half again the cost? The typical cost-conscious evaluator might exclaim, “NO WAY!” and simply purchase the 530 Series instead. This raises the “why” question, for data center workloads we'll need to go a little deeper with a discussion on endurance, end-to-end data checking, power-loss circuitry, the Intel drive controller, and performance consistency.

GB-Day-Writes.pngEndurance testing:

When we endurance test our SSDs, client SSDs are tested with a client workload and data center SSDs are tested with a data center workload. These workloads differ in the way they perform IO to the drives and the data center SSD workload is much more strenuous on the drive the client workload. Put this in context by thinking of SSD endurance as a 26 mile marathon. The client marathon is a relatively flat course with a few small hills; the data center course is runs through mountains and canyons for the entire course. Each of these races takes a different type of athlete, both trained, both skilled, and both experts, but to compare the two by using finish time does injustice to both. The same is true of SSDs specifically designed for the client or for the data center; they are two completely different types of athletes! The SSD you select for your data center needs to be ready for the rigors of the mountain paths.

End-to-end data checking:

Another reason to select an Intel SSD DC S3500 Series drive for the data center would be end-to-end (E2E) data checking and correction. Most drives in the Enterprise IT data center reside behind a RAID controller and are qualified by the major server OEMs (Original Equipment Manufacturers) for production support and warranty. One of the major milestones for product qualification/validation in this space is the E2E correction feature. In E2E data is checked, validated, and corrected if need be internally. This happens at every step of the way; from the point data enters the drive for a write and until it exits the drive for a read. Again with the running metaphor, client drives don’t require this type of strenuous error correction features and the Data Center Series of Intel SSDs meets this requirement. Now we have a mountain marathon runner, who can do error-correction on the trail.

PLI – Power Loss Imminent:

Looking for another reason to select a Data Center Series Intel SSD? PLI is a special feature that looks at the power supplied to the SSD and automatically stops both external and internal IO if it senses a power outage, then makes sure that all the in-flight data is written to the storage media (NAND) using the energy stored in a special super-capacitor. This feature guarantees, in the event of a power outage, that anything an operating system (OS) received an acknowledgement for is physically written to the drive. This is especially important in data center workloads and adds another feature to our mountain runner… the ability to stop the race and save in-flight data.

The Intel Data Center drive controller:

Some people ask about the about differences in the drive controller. In the Intel SSD 530 Series drive, we use a client controller that leverages an internal compression engine to help accelerate client workloads. In our Data Center Series of products, a purpose-built Intel controller does not use hardware compression. Our experience in the data center shows us that many data center workloads are either compressed by the application, or are already in a compressed format when stored in drives. Again, the Data Center Series Family of products was built from the ground up for a data center workload. With this “built for extremes” controller at the runner’s disposal, he can run both the canyons and the flats.

Last but not least, performance consistency:

There’s a difference in the expected duty cycle that client drives and the Intel Data Center Series Family of drives are built for. The data center drive is built to run 100% of the time, its housekeeping activities occur as the drive is operating and this activity does not cause changes in observed performance of the device. With that in mind, the Intel SSD DC S3500 Series drive includes a “Quality of Service” metric in the specification outlining the maximum observed latency up to %99.9999 of the time. In other words, our runner turns in the same marathon time every time no matter the running conditions.

Wrapping this up, if we look at the Intel Data Center Family of SSDs… We have an athlete who’s trained for the rigors of the data center, performs end-to-end data checking, can handle both compressible and incompressible workloads, looks for imminent power outages, and maintains consistent performance under load. In a nutshell, that’s the “why” behind data center class SSDs. The question for the reader now becomes, “Which runner you want on your data center team?”

- Chris

Christian Black is a Datacenter Solutions Architect in Intel’s Non-Volatile Memory Solutions Group. He comes from a 23 year career in Enterprise IT and you can follow his travels on Twitter at @RekhunSSDs.