In-Depth

Evaluating Enterprises' SSD Choices

Here's a look at the three top flash drive types.

• By Scott D. Lowe
• 03/14/2014

With the cost of solid-state storage decreasing to a level that makes it a viable option for enterprises, it's now time to decide which direction your business is going. Here's a look at the three most-popular types of flash-based storage:

Server Side: PCI-e
In recent years, PCI-e-based flash storage adapters have hit the market by storm, offering organizations ways to overcome significant storage performance challenges in the enterprise. The primary benefit to PCI-e storage is that it resides very "close" to the processor and the rest of the components in the server, so storage I/O doesn't have to travel far. This alone can result in substantial performance benefits. Further, by virtue of the PCI-e connectivity, traffic can also avoid delays that might be imposed by storage controllers. As such, this kind of storage offering presents an incredible opportunity when applications demand the lowest possible latency.

There are a couple of different ways by which PCI-e storage adapters can be leveraged:

• As a tier of storage: PCI-e cards can be used as an ultra-fast tier of storage on which organizations store their most latency-sensitive data and applications.
• As a huge cache: In this mode, PCI-e cards acts as a front end to more traditional storage arrays and operate as a read and write cache for those arrays, effectively accelerating that storage.

Verdict: As mentioned, the upside to PCI-e storage is sheer performance and the lowest possible latency, but the downside is the very high cost. Use only when it's necessary to accelerate an external array and for particularly latency sensitive workloads.

Server Side: DAS
Although organizations have tried really hard to eliminate server-based hard drives, in-server and direct-attached storage is poised to make a major comeback thanks to new technologies. In this category, storage manufacturers have built solid-state disks that match the traditional hard disk form factor. These devices connect to the server using traditional SATA and SAS connectivity methods and appear to the operating system as just another storage device.

As is the case with PCI-e-based flash storage, though, there are multiple ways to leverage directly attached SSDs. They can also be used as either a storage tier or as a caching mechanism. These kinds of SSDs tend to be quite a bit less expensive than PCI-e cards, but they're also not quite as fast since there is a storage controller that needs to be used and the I/O is a bit further away from the rest of the computer. Even so, these devices are still orders of magnitude faster than rotational hard drives.

Verdict: These devices are much less expensive than PCI-e when compared on a $/GB basis. When compared to traditional hard drives, the cost of these devices on a $/GB basis is much higher, but when comparing on a $/IOPS basis, these disks could be much lower cost than traditional hard drives. If a use case calls for a lot of IOPS, the SATA-based SSD might be just the solution.

Standalone Arrays
Of course, although many vendors out there are working hard to eliminate the need for a SAN in the data center, the fact remains that the SAN is the most common method by which storage is deployed in today's data center. When deploying flash in a standalone array, there are two real options available in today's market:

• All-flash arrays: All-flash arrays are just that -- storage behemoths chock full of blazing-fast SSDs. These arrays have a lot of capacity since they have many, many drives and they can support hundreds of thousands of IOPS in performance. In order to maximize capacity and bring down the cost per GB, vendors in this space generally include comprehensive deduplication technology that can have a major positive impact on capacity.
• Hybrid arrays: Whereas all-flash arrays offer uncompromising performance, hybrid storage arrays provide the perfect balance of performance and capacity. In these arrays, solid-state disks are leveraged as mega read and write caches, and the system uses these mechanisms to massively accelerate the performance of the rotational storage. One startup vendor sells an entry level array that boasts 22 TB of raw capacity and provides 30,000 IOPS in a single array.

Verdict: For organizations comfortable with external arrays and that might be experiencing performance issues with traditional solutions, hybrid arrays can provide a compelling answer because they balance the need for speed with the need for space.