Western Digital hopes to get hybrid storage right by combining HDD with NAND and a CPU.
Western Digital has announced a new disk drive architecture that combines flash memory with high-density hard-disk drives plus a small CPU to manage everything.
If this sounds familiar, it is. Several years ago there was an effort by WD and other hard-disk drive (HDD) makers to build hybrid hard drives, with small flash drives acting as a cache for the hard disk, but those efforts failed, said Ravi Pendekanti, senior vice president of HDD product management and marketing at WD.
“There was a huge pitfall in those [drives],” he told me. The drives didn’t know what kind of data they had, so they didn’t know that hot data was frequently accessed and should be written on to the flash drive, while warm or cold that wasn’t accessed as much should be written to the disk.
“Not everybody could actually figure out all the time as to where the data should go, or whether it’s hot or warm or cold data, which is why it never took off,” said Pendekanti. “But because of that, we’re able to go forward with the lessons learned and how it’s a different model than in the past.”
The OptiNAND technology combines WD HDDs with iNAND flash memory chips and a special system on a chip (SoC) design from WD. The SoC will manage the storage of data, with live data going to the hard disk while metadata is stored on the iNAND flash. All data storage is managed by the SoC, along with the management of the drive, such as wear leveling of the flash storage.
There’s more to this than a few new chips. WD is talking capacities of up to 50TB by the second half of the decade. It was able to add more capacity thanks to greater tracks per inch (TPI), which means higher storage density, coupled with the fact that metadata is written to the NAND rather than the disk like it is today. Hard drives can generate gigabytes of metadata, and retrieving and writing it means the hard disk, already the slowest component in the computer, is slowed further from performing its main functions.
“So with these two in play, we are able to get more capacity. So instead of metadata taking up more space on your disk, and the fact that it goes in conjunction with adding more TPI that is giving rise to a higher areal density,” he said.