Seagate to Expand Usage of SMR

Today, the vast majority of HDDs are based on perpendicular magnetic recording (PMR) technology, which is sufficient for today’s applications in terms of areal density and performance. Several years ago makers of hard drives believed that PMR technology would not support areal densities of over 1 Tbit per square inch (Tb/inch2) because of physical limitations and yields. However, in the last couple of years, a lot of progress has been made and it looks like PMR technology will continue to evolve towards that goal (albeit slowly).

To increase areal densities significantly, Seagate started to use shingled magnetic recording (SMR) technology several years ago. The SMR technology enables areal densities higher than 1 Tb/inch2, but brings a number of challenges. HDDs that use shingled recording write new tracks that overlap part of the previously written magnetic tracks. The overlapping tracks may slow down writing because the architecture requires HDDs to write the new data and then rewrite nearby tracks as well. For this reason, Seagate’s implementation of device-managed SMR groups adjacent tracks into bands, where shingling ends. This optimizes the number of tracks that need to be rewritten after writing operations and thus promises to help provide deterministic and predictable performance of SMR HDDs in typical scenarios. Ultimately, environments that involve a decent amount of writing might not be impressed with SMR performance, but the key figure here is density.

Grouping into bands is not the only way to conceal peculiarities of SMR. In fact, every SMR drive has zones that use PMR recording technology with relatively fast writes. Those zones are used to quickly record data and perform other necessary operations when needed. Eventually, information from PMR zones is automatically moved to SMR zones without any actions from the user or the operating system. One can think about it as some sort of garbage collection that needs to be triggered by the firmware. Seagate does not disclose actual configurations of its SMR bands or capacity of PMR zones, but notes that such configurations depend on types of applications that the HDDs are designed for (i.e., consumer drives and drives for cold storage have different configurations).

To further ensure optimal writing performance, SMR-based HDDs can also integrate DRAM and/or NAND flash buffers. For example, Seagate’s Mobile 2.5”/7mm hard drive with 2 TB capacity has a 128 MB DRAM cache and an unspecified amount of SLC NAND flash memory. The SLC NAND buffer has a rather high writing performance, which means that when small amounts of data are recorded on an SMR-based drive, the latter can boast with a very high write speed. Since the amount of NAND flash is not very high (less than one gigabyte in the case of the mobile 2.5” 2 TB HDD), it does not help a lot with large files, but for a typical home user storage environment it should be helpful.

One of the areas Seagate is proud of is the iterative product design for optimizing writing performance of SMR-based drives since the company first introduced them several years ago. One might argue that the claimed performance numbers for the Seagate Archive 8 TB and Seagate Mobile 2 TB are not that impressive. This hides the implementation of SMR management in the Seagate Mobile 2 TB, which involves three levels of caches/buffers (DRAM, NAND, PMR zones), and demonstrates the complexity of such HDDs. The architecture of SMR-based consumer drives requires controllers with advanced computing features to manage buffers, transfer data from PMR zones to SMR zones and perform other operations to guarantee expected performance in different workloads. We have seen similar problems with TLC NAND-based SSDs, which use pseudo-SLC buffers to ensure fast writes. Depending on Seagate’s plans for the future, the device-managed SMR HDD architecture seems to be expandable for future performance benefits.

Seagate plans to adopt SMR rather widely going forward. In the near future, Seagate will introduce SMR-based HDDs specifically for video surveillance applications (Western Digital's Purple line of HDDs spring to mind as the competition there). Later on, more hard drives featuring “shingled” platters for client PCs can also be expected. We are not sure whether SMR-based HDDs are set to be offered to performance-demanding applications given the evolution of PMR and inevitable emergence of other technologies, but we might see hybrid variants that a partial SMR and partial PMR to keep performance high. Still, Seagate made it clear that SMR is not reserved for cold storage.

The Evolution Continues, New Challenges Arise Helium Will Remain Exclusive for High-Capacity Applications, For Now
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  • Ushio01 - Wednesday, July 06, 2016 - link

    I wonder how much of this will ever reach market? as SSD's take over ever more of the storage market the remaining HDD manufacturers will be required to spend ever more on R&D while dealing with shrinking revenue. Reply
  • DanNeely - Wednesday, July 06, 2016 - link

    The consumer HDD market is slowly imploding, but while it's roughly half of all drives sold that's not where the money is. The Enterprise HDD market is doing better. Sales are down a bit; but while Seagate/WD/Toshiba don't break the two segments of enterprise drives out, it's probably from SSDs chewing into 10/15k drives in servers not the high capacity 3.5" drives used for bulk storage. Seagates comments about the next gen of 15k drives potentially being the last tends to back this up, since they're talking about multiple generations of other drive types.

    Bulk data storage will stay with spinning rust until the price per GB crosses over in SSDs favor. Estimates I've seen on that a year or so ago were looking at 2025; but there's a fair amount of speculation there since the results of a half dozen generations of tech in each platform are somewhat speculative.
    Reply
  • Anato - Wednesday, July 06, 2016 - link

    That patent [1] is clear example how current patent system is out of control and not useful to society at large. Short recap, patents original idea was to give temporal monopoly to inventor who disclosed his invention. There was no right to own anything you invented, but it was seen that disclosing the invention would ultimately benefit society who, after temporal monopoly, could use the invention.

    Now opposite is true, there is nothing useful disclosed in Seagates patent! But we grand Seagate sole ownership to use Gold with Cu, Rh, Ru, ... or Mo in concentrations of 0.5-30% in HAMR NFT. How does this benefit us?

    Of course Seagate can't stop WD to use same alloys as WD have similar patents to sue back, but they both can stifle smaller competitors. I don't think there will be any more competitors in HDD space, but same applies to other fields and their patents.

    [1] http://www.google.com/patents/US8427925

    [Disclosure, I didn't read full patent application, did cursory review and didn't find anything of value]
    Reply
  • Zak - Wednesday, July 06, 2016 - link

    I was wondering why HDs never broke the 7500rpm and 15000rpm barriers. Reply
  • DanNeely - Wednesday, July 06, 2016 - link

    For consumer devices: noise. 10/15k HDDs are obnoxiously loud like an >40x CD or >16x DVD drive; except that they're spinning constantly not just for the few minutes it takes to read/write them. On the enterprise side, I'd guess implementation difficulty; probably due to vibrations was the limiting factor. If not mechanical strength of the platters themselves was probably the issue. Top end centrifuges can go to at least 70k RPM; but can be built much more heavily than a thin platter can. Reply
  • metayoshi - Wednesday, July 06, 2016 - link

    Not just noise, but heat. In a constrained system like a laptop or desktop, the spindle and vibrations cause a ton of heat to be generated. Just look at WD's last consumer 10k drive, the 1 TB Velociraptor. It's a 2.5" drive that comes with its own heatsink for 3.5" bays. You definitely can't put that in a laptop, and it hits a market in the desktop space which has pretty much been taken over by SSDs. Reply
  • piasabird - Wednesday, July 06, 2016 - link

    Still using hard drives. No reason to switch when hard drives are so cheap. When I watch TV on the Internet, It still works so no reason to change. Reply
  • pavag - Wednesday, July 06, 2016 - link

    Kurzweil curse.

    Nobody accounts the relative speed of price reduction. SSD will get cheaper per gigabyte than SSD before 2020.

    We will never see HDMR HDD. And there is a chance we will not even get HAMR.

    And article speculating about the date when SSD will beat HDD for price per gigabyte would be interesting.
    Reply
  • serendip - Friday, July 08, 2016 - link

    I'm not sure about this. On my laptop, I've got a 120 GB SSD I got ages ago along with a recent 2 TB drive. Both cost about the same when new. I think HDDs will continue to get bigger and cheaper faster than SSDs, at least until some new process tech allows for very high flash densities and low production cost.

    The main issue is price. There are still lots of users (like me) who can't afford huge multi-TB SSDs to hold everything, so they have to make do with a boot SSD and a storage HDD.
    Reply
  • jabber - Wednesday, July 06, 2016 - link

    So you didn't bother to ask why Seagate's HDD reliability has nosedived since the floods a few years back? Reply

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