Recent articles from several large websites have highlighted the performance of consumer SSDs in relation to enterprise SSDs. Many times these articles have declared that client SSDs can equal, or beat, enterprise SSDs. The fact that a bit of overprovisioning can produce higher IOPS or bandwidth has nothing to do with the true measurements of performance consistency, and with comprehensive study these theories are debunked when measuring the latency of all I/O's issued during the testing period. The focus needs to be placed back on latency.
We are pleased to see that many of our competitors have embraced our scatter testing, this provides us a measure of validation from our peers; but it is distressing to see these same techniques used as a means of disseminating incorrect analysis of the results. Some caveats of performance aren't always revealed even when using sophisticated scatter testing.
A key take-away from our testing revolves around the ambitious specifications touted by consumer SSDs. Client SSDs promise massive IOPS in pure read workloads, but once we begin to mix in even the lightest of write workloads, performance plummets. There simply are very few pure read workloads in the vast majority of enterprise deployments, and client SSDs do not handle mixed workloads as well as SSDs designed for enterprise environments.
Enterprise SSDs really come into their own in pure write situations due to a thoroughbred design optimized for heavy usage, but there are also very few pure write workloads. The real performance lies in the middle ground, and in this region enterprise-class hardware is unassailable.
Latency is the primary driving force behind SSD usage and delivers radical performance gains over typical HDDs. When placed in enterprise environments, our testing revealed client SSDs faltered tremendously in latency QoS.
To put this in perspective, a single 15,000 RPM MK01GRRB/R Toshiba HDD had 11,748 I/O's fall into the 600-800ms latency range during the exact same 8K random write test utilized in this product evaluation. In comparison, the 840 Pro had 3,328 I/O's in the 800-1000ms range, and the Vector had 2,777 I/O's fall into the same 800-1000ms range, higher than the 15K HDD.
These outlying I/O's can be crippling to application performance in actual deployment. Even though the percentage of operations for the client SSDs are very small, the fact that we are experiencing worse latency with some operations in comparison to an enterprise HDD is telling. The client SSDs will be faster overall due to the increased number of overall fast operations, but there are situations where an application waiting on data will wait longer than they would from an HDD. This really drives home the performance gap with client SSDs. The Optimus had zero operations above 40-60ms in the same test. This is the most powerful evidence of the difference between enterprise and consumer SSDs.
Utilizing extra overprovisioning with client SSDs is a common approach to boost steady state performance, but even with hefty overprovisioning, there are still a number of operations that fall into an unacceptably high latency range. Look at TweakTown soon for an upcoming article on the effects of overprovisioning.
Overprovisioning a client SSD also dilutes the dollar per GB advantage. Factoring in the higher price per GB after overprovisioning brings the number of other features provided by enterprise SSDs into focus. Once the price per GB begins to come close to enterprise SSDs, features such as power loss protection and enhanced data protection quickly tip the scales in favor of the enterprise SSD.
Many users forgo the enhanced data protection of enterprise SSDs in favor of utilizing consumer SSDs in RAID arrays, defraying the heightened potential for data loss and aggregating performance of multiple SSDs. Unfortunately, the speed of the entire array is constrained to the speed of the slowest I/O. In RAID arrays numerous client SSDs can equate to simply terrible performance in relation to enterprise SSDs. This is due to the effects of a continuous steam of errant I/Os from multiple drives and the array is constrained to the speed of the slowest operation.
SSDs bring tremendous advancements in the IOPS produced per Watt of energy consumed. Enterprise SSDs typically enjoy large advantages in the IOPS per Watt category, and provide enhanced power efficiency.
There are a number of applications where client SSDs make sense, but they are usually in workstation and consumer applications. The comparison drives tested are the fastest client SSDs on the market and in a consumer environment are hard to beat. It really isn't fair to put them in the ring against a heavyweight like the SMART Optimus, but they were selected for their class-leading status. We required the best SSDs that the client-side had to offer, and the OCZ Vector and the Samsung 840 Pro fit the bill.
In certain situations, we received results worse than a 15K HDD. There simply is a tremendous gulf between the performance of these two solutions, especially when we go beyond the typical 'speeds and feeds' and drill down into the real performance measurements that have a dramatic impact on application performance and TCO.