WD HDDs with Embedded Flash Increase Capacity, Resiliency

Western Digital has announced new flash-enhanced hard drive architecture that analysts say will be an important step forward for capacity, performance and reliability. This smarter, faster, denser storage drive could reach an estimated 50TB of capacity by the end of the decade.

The new storage architecture is based on the company’s OptiNAND technology that inserts an iNAND embedded flash drive (EFD) into its hard disk drives. This is different from previous hybrid drive technology, where Western Digital inserted some flash into HDDs and used it as a caching tier, noted Eric Burgener, a research vice president with IDC’s enterprise infrastructure practice.

“As HDDs service I/O, they handle a lot of metadata operations, with more random workloads being more metadata-intensive,” he explained. “When the drive has to access the metadata off of the drive spindles, it requires more head movement and introduces additional latency. Putting all the metadata in the EFD allows metadata operations to get handled at least an order of magnitude faster, and lets the drive heads focus on servicing user data requests, not metadata.”

Part of the embedded flash drive capacity is also used as a write cache, so the HDD can now return an acknowledgment back to the requesting application once the EFD responds instead of waiting for the I/O to get written through to an HDD platter. It’s the combination of these two capabilities that boosts performance while maintaining data integrity, Burgener said.

Higher Performance and Better Resiliency

The iNAND technology also improves resiliency. Traditionally, write-through caches were slower but guaranteed data integrity if a device failed, compared with write-back caches, which had better performance but could cause small amounts of data loss if the drive failed. iNAND provides the best of both worlds, Burgener said: higher performance with better resiliency.

Capacity also gets a boost with the new technology. Western Digital is starting by shipping

samples of a nine-disk, 20TB, flash-enhanced drive with OptiNAND and energy-assisted perpendicular magnetic recording (ePMR) technology to some customers, but expects to reach 50 terabytes by the second half of the decade.

“It’s the ePMR that gives the technology air density, which in turn allows the technology to store more data. That, in turn, sets up a longer term roadmap for larger HDDs, which traditionally has been harder and harder to achieve as aerial density or capacity for disk achievements have slowed,” said John Chen, vice president of TrendFocus.

So far, Western Digital is the only vendor that has announced this approach. Competitors such as Seagate and Toshiba have introduced other technologies that boost some combination of performance, resilience or capacity in their HDDs. However, both Seagate and Toshiba are working on similar class drives, but may use different technologies to get there, Burgener said.