Instead of promising SSD-like speeds thru caching of consumer facts, OptiNAND gives extended areal density by way of disposing of firmware-accessible metadata from the disk itself and storing it on NAND instead.
20TB per disk without SMR
The most tangible milestone carried out via Western Digital’s newly announced structure is a nine-platter, 20TB pressure that does not require Shingled Magnetic Recording (SMR) strategies.
The metadata we’re speaking approximately isn’t always filesystem metadata—it’s hardware metadata, accessible by means of the pressure’s firmware but not uncovered outdoor the drive itself.
Repeatable Runout (RRO) is a description of a rotational gadget’s inaccuracies that may be expected in advance of time—as an example, a steady wobble because of the microscopically imperfect alignment of a rotor. RRO statistics is precise to each individual pressure and is generated on the factory for the duration of manufacturing and stored on the disk itself.
In typical conventional drives, RRO metadata is interleaved with purchaser-available records on the platters themselves, reducing the overall areal density of the disk because of decreasing the wide variety of tracks in step with inch (TPI) to be had for consumer facts. OptiNAND structure permits Western Digital to move this metadata off the platters and onto the onboard NAND.
In order to hit 20TB on a nine-platter pressure with cutting-edge recording technologies, you want a next-era “edge” of a few type. In closing 12 months’s 20TB drives, that edge was SMR—in this yr’s most modern models, it is OptiNAND.
- Sync write acceleration
- On this Seagate Ironwolf NAS disk, sync writes are an order of value slower than async. OptiNAND need to eliminate most people of that overall performance bottleneck.
- Jim Salter
- Although Sivaram opened up our interview putting forward that OptiNAND isn’t always for storing customer information at all, there may be one exception—the contents of the power’s DRAM cache can be flushed to OptiNAND inside the event of an sudden electricity loss.
This has a massive impact at the force’s overall performance whilst the power is asked to perform sync writes—a special mode of operation commonly requested by way of databases, virtual machines, and maximum NFS exports. When an application requests a “sync write” to a force, all of the normal write aggregation and caching operations emerge as unavailable—the utility tells the operating system, “I’m not doing some thing else till you verify that this facts is saved completely and competently on disk.”
OptiNAND structure permits drives to complete those sync() calls instantly with out lying approximately the safety of sync write statistics. Instead of pausing the whole lot the force is doing to are searching for the heads to the proper locations and write the facts to the magnetic medium, the pressure can actually say, “Your facts is secure” as soon as the writes are everyday into the pressure’s own DRAM buffer.
Normally, this will be taken into consideration an risky violation of write barrier mandates. But on the OptiNAND drives, as much as 100MiB of “cache-disabled” writes can be ordinary into DRAM due to the fact, in an emergency strength-off event, the drive’s onboard capacitor can hold the DRAM viable for long enough to flush the write cache to OptiNAND. On restoration of energy, the dirty records quickly written to OptiNAND is study lower back and without delay devoted to rotational garage.
Use instances and availability
According to Sivaram, the new OptiNAND drives may be useful everywhere traditional tough drives are used.
Allowing the power to “fudge” on write limitations by using counting on capacitor power to flush dirty writes from DRAM to OptiNAND can improve performance for the ones writes extensively—in lots of cases, likely with the aid of a thing of ten or extra.
The 20TB OptiNAND disks are presently in the early levels of production, with samples delivery to pick Western Digital enterprise customers simplest. However, the technology is anticipated to function “the foundation for destiny designs and improvements” across Western Digital’s whole rotational garage product line, with marketplace-unique products turning into available later this yr.