Solid state drives are not all alike. Solution providers are faced with many competing products. Here, Teresa Worth, Senior Product Marketing Manager at Seagate Technology discusses how to discern which one is right for your customers' needs.—Jennifer Bosavage
Growing numbers of VARs and IT solution providers are turning to solid state drives (SSDs) to meet increasingly rigorous storage performance requirements for write-intensive enterprise applications. SSDs offer dramatically higher performance than traditional hard disk drives (HDDs) because the way they record data is purely electrical and, therefore, almost instant. In contrast, HDDs use a much slower process involving mechanical seeking heads to read and write digitized data on rotating platters.
While the typical enterprise class 15K RPM HDD achieves 350 IOPs for random writes and 400 IOPs for random reads, an SSD can push up to 15,000 IOPs for random writes and 50,000 IOPS for random reads. Enterprise SSDs also best client SSDs in responding to data requests, performing four times faster with a response speed of less than 5 ms compared with more than 20 ms for a client SSD.
Such high performance is driving rising data center adoption of SSD technology. According to the Gartner Group, the enterprise SSD market grew from approximately 320,000 units and $485 million in sales in 2009 to more than 1 million units and more than $1 billion in sales in 2010. Gartner forecasts that the enterprise SSD market will mushroom to 9.4 million units and $4.2 billion in sales by 2015.
To thrive in serving the enterprise market, VARs and IT solution providers must first be able to distinguish between different types of SSDs with vastly different performance and endurance attributes for the consumer and enterprise markets, and then select the enterprise solution that best meets the needs of their customers.
Different SSDs for Different Workloads
Client applications for SSDs include entry-level servers, laptops, cameras, PCs, and mobile phones. Enterprise SSD workloads include heavy analytics, web indexing, OLTP and database warehousing, medical imaging and video editing/processing, and high-compute servers. Client SSD applications typically serve a single system used no more than eight hours a day, five days a week on small datasets in read-intensive operations, performing two to three full drive writes a day. In contrast, enterprise SSDs run round-the-clock every day of the year, with multiple users performing write-intensive operations (more than 10 full drive writes per day) characterized by complex data patterns on large datasets.
To meet the demands of these exacting data-center workloads, SSD manufacturers must deliver products with enterprise-class endurance and performance while satisfying stringent requirements for device interoperability and customer support.
To start, enterprise-class SSDs must be consistent in delivering both high IOPS and low response times to enable data centers to meet service-level agreements. Yet SSD performance can be highly inconsistent. While read and write speed for new SSD drives is exceedingly fast, performance often drops over time because data must be erased before being overwritten. While SSDs can read and write 4KB in a single pass, they can erase only 512KB at a time. That mismatch poses no problem when the drive is new and has considerable free capacity but tends to bog down write speeds as the device fills with data.
Newly minted industry SSD performance standards can help VARs compare the read/write performance and response consistency – key measures of enterprise performance – of devices offered by various vendors. Chief among these new storage standards are the Storage Performance Council’s SPC-1C and the Enterprise Solid State Performance Test Specifications (SS PTS) from the SNIA Solid State Storage Technical Work Group, which works closely with the SNIA Solid State Storage Initiative.
Endurance and Data Integrity
Enterprise applications are extremely write-intensive, making high endurance – the total amount of data written to a device during its lifetime – an essential characteristic of an enterprise SSD. The number of writes possible to NAND flash memory cells on SSD drives is finite (referred to as their write/erase life), so the cells tend to wear out. When they do, the device becomes unreliable and the integrity of the data is at risk – compromises that are unacceptable in enterprise environments.
Single level cell (SLC) NAND flash, in which one bit of data occupies one cell of flash memory, has a limit of about 100,000 write/erase cycles. In contrast, multi-level cell (MLC) NAND flash, which until recently was used primarily for consumer devices, has far lower write/erase thresholds (typically around 10,000 write/erase cycles for 2-bit-per-cell NAND and 1,000 to 3,000 write/erase cycles for 3-bit-per-cell NAND), making them inadequate for the rigors of enterprise environments.
To take advantage of the lower cost of MLC flash, many vendors are now introducing MLC-based SSDs for the enterprise, though the endurance and data integrity capabilities of the devices vary widely. To safely overcome MLC limitations, vendors should:
VARs can test vendor endurance claims by taking advantage of new SSD endurance testing standards from the JEDEC Solid State Technology Association: The JESD218A Solid-State Drive (SSD) Requirements and Endurance Test Method and JESD219 Solid-State Drive Endurance Workloads standards define specific requirements for enterprise and client application classes, describe a test methodology, and create an SSD endurance rating that makes it easy to compare devices for endurance.
With the high cost of SSDs, many data centers are deploying SSDs in a tiered environment with HDDs. Tiering automatically places data on the storage medium that is best suited for current access patterns, matching the speed and cost of the storage device with the importance and access frequency of the data. To simplify the management of a tiered environment that incorporates both HDDs and SSDs, VARs should select SSD devices that follow industry standards and offer identical features to those found on HDDs. For example, by standardizing on SSDs with a 2.5-inch form factor, SAS interface and the same self-encrypting drive technology, data centers can reduce complexity and cost.
Partnerships and Support
For VARs, choosing the right vendor partnerships is critical. As NAND flash device deployments in enterprise data centers continues to increase, VARs need to work with vendors that understand the needs of large enterprises and are equipped to serve them. Vendors should have extensive expertise in enterprise storage and the technical resources necessary to support the complex and expensive product certification process, along with a global support and distribution infrastructure. To minimize the high cost of qualification and total cost of ownership, VARs should look for SSDs with the highest endurance rating. Many enterprise SSDs are designed to last twice as long as client SSDs and the warranty terms – 5 years for enterprise SSDs compared to 3 years for client SSDs – reflect this difference in lifespan.
VARs and IT solution providers offering SSDs also need to be sure that the devices and surrounding support infrastructure meet the enterprise requirements of their customers. A careful balancing of SSD performance, endurance, interoperability, and support directly impacts total cost of ownership and should be considered as SSDs are designed into solutions that satisfy increasing demands on the data center.