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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  • drothgery - Saturday, July 09, 2016 - link

    It's complicated. There's a minimum cost to build any mechanical hard drive, and the cheapest possible flash storage device is cheaper than that. That's why you don't see HDDs in any applications that need less than 128 GB or so anymore. It's just that the marginal cost of additional capacity is lower with hard drives (at least, until you start figuring in complex TCO arguments for data centers with very large amounts of storage). Reply
  • zodiacfml - Sunday, July 10, 2016 - link

    It is almost irrelevant due to economies of scale. Right now, HDD are still comfortable with their scale right now. They have to be scared as it might drop non-linear in a few years; their drives will become more expensive that they will have to produce fewer, larger, archival drives. Reply
  • AnnonymousCoward - Sunday, July 10, 2016 - link

    "almost irrelevant"? HDD's entire play is cost/GB, and there's reason to believe they cost MORE below some capacity.

    "economy of scale" - you mean volume? Samsung already ships >10B memory chips per year, far more than Seagate units.
    Reply
  • Danvelopment - Sunday, July 10, 2016 - link

    Hard drives will remain as long as price/GB stays well ahead of solid state.

    Seeing as manufacturers have been unwilling to maintain that for the last 4 years, all I can see is a death spiral.

    I bought 3x 2TB HDDs in 2012 for $99NZD each. The current cheapest 2TB HDD is $115. And the cheapest HDD or GB is a 3TB at $156 (slightly more/GB).

    Fark HDD manufacturers. They can't win on performance or reliability against Samsung SSDs, all they can do is win on price but that gap has shrunk so much in four years I don't hold much hope for them without a drastic move. SSDs don't have to reach the same price point to take over, they just need to be close enough when accounting for the performance gap.

    It also doesn't help that they've already lost the density crown and in a much smaller form factor.
    Reply
  • Bobs_Your_Uncle - Tuesday, July 12, 2016 - link

    Just now (7/12/16 @ 19:17EST) heard on The Nightly Business Report (PBS) that Seagate:
    - announced earnings that exceeded analyst expectations
    - raised their projected income guidance
    - experienced their "best day ever" in the markets (measurement metrics not disclosed)

    ... oh yeah ...

    and Seagate announced that they're eliminating 6,000 jobs ...

    The future is certainly looking rosy ... I guess ...
    Reply
  • neatfeatguy - Thursday, July 14, 2016 - link

    I hear Seagate is looking to close out a major branch location nearing the end of the year or start of Q1 2017. Location in Shakopee, MN or a China branch (sorry, I didn't get what location in China.....rumor is pointing to MN location so far and as early as start of December has been hinted).

    Makes you wonder how well things can really be going for them - unless this is a restructure to help them stay viable in the every fast changing world of storage technology.
    Reply
  • truemore - Thursday, July 28, 2016 - link

    So I was having a meeting with one of the large corporate storage providers asking when they thought the "mass change" would happen from HHD to SSD for corporate storage.
    Interestingly even their technology people were surprised, but at the enterprise level the inflection point happened this year for primary storage devices. Given much better TCO over time and vast performance improvement with SSDs they have better short and long term ROI due to a better than expected 40% decrease in price per TB in the past 12 months and the large jump in maximum enterprise SSD size.
    According to their people they are pushing all customers as fast as possible to SSD for all hot, and most warm storage. For them it makes perfect sense since they have very few drives break, arrays can easily be upgraded lowering the number of RFPs per $ sold and the performance increase for the customers is frankly amazing in the enterprise compute environment.
    I wonder how this shift will affect us on the bottom, since large storage providers suck a large portion of the overall storage market. They may be the 600 gorilla that forces the market to make a quick move off of HDDs,
    I would also be curious how the better performance and longer life span of SSDs will hurt SSD/HHD producers over the long haul since there will be much fewer sales over the long term.
    Reply
  • Gothmoth - Saturday, July 30, 2016 - link

    what i want from HDD´s is REABILITY, REABILITY, REABILITY.

    it can´t be that 10+% o harddrives from seagate die on me in the first 6-8 month.
    i have a small renderfarm at home and 8 sytems with 2-4 harddrives each.

    infant mortality of HDD´s is a real problem. and overall REABILITY seems to be getting worse.
    Reply
  • Gothmoth - Saturday, July 30, 2016 - link

    sorry i meant RELIABILITY... :-) Reply
  • profquatermass - Monday, August 29, 2016 - link

    Oh the Irony...... Reply

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