Tip

Solid-state drives a good fit for critical transactions

Service provider takeaway: Even with their high price premium, solid-state drives allow service providers to deliver significant savings to customers by shaving milliseconds off critical transactions.

Are your customers constantly complaining that their storage isn't fast enough? Are they buying lots of small, high-rpm drives for time-critical transactional databases? How would they respond to technology that provides 30 times more input/output operations per second (IOPS) than 15,000-rpm Fibre Channel drives? After years of concerns about speed and reliability, this technology -- the

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solid-state drive (SSD) -- is finally eliminating the slowest component in transactional databases: the disk drive.

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Solid prospects for solid-state drives

Today, SSDs are about 50 times more expensive per gigabyte than a 15,000-rpm drive. You may think that your customers would never pay that price for performance -- but speed is worth big money for many companies. Many brokerage houses, for example, pay huge penalties on trades that aren't processed within a specific service-level agreement (SLA). At other companies, faster-responding business analytics engines could enable near-real-time feedback for advertising or product placement changes, driving multimillion-dollar, time-sensitive business decisions. So if shaving milliseconds off critical transactions can make your customer money, they'll want to know more about solid-state drives.

The timing of such discussions with customers is good, since the solid-state drive market is gaining momentum. For instance, EMC's recent announcement of SSDs for high-end arrays, enabling tiered storage -- SSD to Fibre Channel to SATA -- in a single box, is likely to spur other similar announcements.

Solid-state drives deliver speedy response

So how does solid-state technology improve upon disk? Solid-state storage I/O performance is linear, meaning that the SSD disk response times remain consistent all the way to their maximum I/O capability. In comparison, traditional disk drive response times get progressively worse as IOPS increases.

But solid-state storage isn't new -- cached disk arrays have been buffering slow disk drives with fast memory for decades. The problem was that memory was much more expensive than spinning platters. When cost didn't matter, memory as primary storage was still tough to justify because nonvolatile memory just wasn't fast enough. To protect the performance and data integrity of the data, solid-state storage was often just fast volatile memory front-ending traditional disk drives.

The only real difference between solid-state storage and cached disk arrays was that solid-state storage has a 1:1 ratio of volatile memory to backup disk space, while cached disk arrays used algorithms to try to intelligently prefetch data into smaller memory pools. Even in cached disk arrays, most high-end versions could pin a drive in cache, allowing selective volumes to be in essence solid-state.

Some niche players, such as Texas Memory Systems, have developed 100% solid-state storage arrays. But they require you to put 100% of an application's data on SSD or spread it across SSD and traditional arrays to tier within a database. There weren't many good hybrid solutions.

Recently, though, EMC changed the dynamics by announcing SSDs for its DMX4 high-end storage array. Now a single box can provide a tiered storage architecture, including Tier 0 SSD to Tier 1 and 2 Fibre Channel and Tier 3 SATA drives. Others will surely follow because the value proposition is simple: A single database may have many regions of data, each requiring different performance characteristics. Indexes may benefit from the supreme performance capabilities of Tier 0 SSD, and the same database may have archive regions living on Tier 3 1 TB SATA drives. One application, four tiers of storage, all in one box: That may captivate your customers.

Good candidates for SSD

Despite its obvious performance appeal, SSDs are still a lot more expensive than traditional storage and they're not a good fit for all data. To help your customers benefit from solid-state drive technology, you have to know when it's appropriate.

Look for SSD opportunities in direct line-of-business applications like financial trade clearing systems, where increases in performance can reduce risk or improve revenue opportunities for the customer. It is likely that your customers have been striping lots of small disks and only using a small amount of the storage on each drive to guarantee a certain access density. Customers who have done this already may be able to reduce the cost impact of implementing SSD by reclaiming those striped and underused disks for normal storage.

The critical, time-sensitive applications that justify SSD will probably be transactional databases with small and/or random read/write profiles. High-transaction databases usually have small (4 KB to 8 KB) records that are accessed randomly, making disk array cache prefetching and read-ahead algorithms ineffective. SSD, on the other hand, is well-suited to such access rates. These databases may also frequently log read access for replication or rollback transactions -- both of which are random reads and could benefit from SSD. Finally, business-critical transactional databases don't get a lot of downtime and may be highly fragmented. Fragmented databases produce random I/O, causing disk drives fits while solid-state drives soar.

It's important to note, though, that solid-state storage isn't always about performance. Sometimes it makes sense in niche applications that require ultra-high reliability. For example, SSDs are already common in aerospace applications, high-vibration environments and desolate locations like Antarctica. This is because solid-state drives have no moving parts, which usually translates to a higher mean time between failures (MTBF). These high levels of reliability may be necessary in remote or inaccessible locations, as well as under extreme temperatures, pressures and g-loads. SSD is also a good fit in mobile applications where normal disk storage just won't work.

Even with the higher cost per gigabyte of solid-state storage, customers may be able to save money by improving performance or reclaiming underutilized performance disks and replacing them with solid-state drives. The best plan is to present the performance and pricing data to your customers and let them decide which technology best suits their needs.

About the author
Brian Peterson is an independent IT infrastructure analyst, with a background in enterprise storage and open systems computing platforms. A recognized expert in his field, Brian has held positions of responsibility on both the supplier and customer sides of IT.


This was first published in July 2008

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