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Most enterprise storage systems are now all flash-based, particularly in the case of primary data storage. Yet, in these budget-strapped times, it pays to look at drives that blend flash SSDs with hard disks to provide extra secondary capacity at an affordable price. Multiple vendors offer these solid-state hybrid drives, which combine a traditional high-capacity HDD with high-speed SSD technology.
Hybrid storage adoption is growing rapidly as enterprises look to trim expenses in a suddenly shrinking and more challenging economy.
But before committing to a solid-state hybrid drive (SSHD), it pays to understand the advantages and weaknesses of a hybrid drive vs. SSD.
How hybrid drives and SSDs compare
Hybrid storage devices are designed to blend hard drive utility with the speed, reliability and energy efficiency of SSDs. SSHDs include a small amount of flash in combination with the core hard disk architecture.
The high-speed SSD portion of the drive acts as a cache buffer for data that's frequently written to or retrieved from storage. That frequently used data gets served from the flash part of the drive, providing SSD-level performance for the data and accelerating application workloads.
SSDs are fast and can supply the same amount of storage as traditional hard drives, yet they cost from five to 20 times as much as hybrid drives, depending on their storage capacities, noted Curtis Buhrkuhl, senior professional services engineer at managed services firm Office1. "Full solid-state drives use NAND memory chips to make them so fast ... and even the smaller version used in hybrid drives is enough to make noticeable improvements to how fast the storage device can run," he said.
Cost savings is what drives most enterprises to consider SSHD adoption when making the hybrid drive vs. SSD comparison. "All-SSD racks are too expensive and, on their own, they still don't provide the best capabilities of hybrid," said Patrick Hubbard, principal head geek at IT management software provider SolarWinds. Many hybrid drives automatically optimize the media mix based on usage, deduplication, automated backup and single point monitoring. This approach enables hybrid drives to keep costs down while increasing flexibility and performance, he said.
Although cost is often the initial driver behind SSHD adoption, the idea of combining multiple storage technologies, each addressing a specific storage need, is becoming increasingly popular. "With vendors bridging disk and flash with cloud and [hyper-converged infrastructure], hybrid can combine local magnetic, flash and remote storage into blended services," Hubbard said.
Basic SSHD deployment is relatively simple. The devices are typically packaged as single units. Additionally, most SSHDs come with self-optimization capabilities enabling the device to learn independently which files to cache for enhanced performance.
"They also give you the choice to enable a 'host-hinted' option that will provide hints for you to manually program the device yourself, if you want more control over what gets moved into the separate cache," Buhrkuhl said. Given that SSHDs don't require additional equipment to use, they're good options for both traditional and remote workforces.
Hybrid drive drawbacks
For all their benefits, SSHDs also present some disadvantages. "If leveraged properly by an application, a hybrid drive can provide the high-performance benefits of an SSD at close to the lower costs of an HDD," said Greg Tevis, vice president of global strategy at SaaS-based enterprise data protection technology company Cobalt Iron. However, "if the SSD isn't effectively used by the application, you might be underutilizing the SSD and overpaying for the storage," he said.
While a hybrid drive's SSD and HDD storage functions can be manually configured and allocated to applications, that's generally not a good idea. "This static allocation approach requires deep storage expertise, introduces operational complexities and would not optimally leverage the SSD investment," Tevis said. A better practice is to let the drive's software automatically manage the SSD and HDD storage.
SSHDs also have an unusual quirk that isn't serious over the long term but can confuse new adopters. Initially, the SSHD may run only about as fast as a regular hard drive. This is because hybrid drives go through a break-in period during which they learn which files and programs are used most frequently. Those files and programs are moved to the SSD cache where they can be retrieved almost instantly, Buhrkuhl said. "This is temporary; once the device learns what files to place in the cache, you will notice it runs much faster than a typical hard disk drive," he said.
Hybrid storage also shares a drawback with many other leading-edge IT tools: increased complexity. "Even in a packaged solution, there are more elements to configure and monitor, more things to break and new skills to master," Hubbard said.
The advantages and disadvantages of using hybrid drives vs. SSDs will vary from organization to organization. As with any technology, it's important to monitor SSHD use and performance. "The only way you can prove ROI, especially with an outlier cost and briefly disruptive transition like hybrid, is to have metrics before and after deployment," Hubbard advised. Data demonstrating improved performance and suitability to task is an important part of demonstrating the effectiveness of hybrid drives, he added.