back to article Seagate's lightbulb moment: Make read-write heads operate independently

Seagate is increasing IO performance in disk drives by separating read-write heads into two separate sets which can operate independently and in parallel. The heads are positioned at one end of actuator arms which rotate around a post at their other end to move the heads across the platter surfaces. Thus, with an eight-platter …


  1. A Non e-mouse Silver badge

    Whodathought it - large individual drives suck at random I/O performance.

    I seem to recall this being brought up when 1GB drives were first coming to market: An array of lots of smaller drives has better performance than the same sized array with fewer drives.

    1. Gordan

      '90s Called...

      ... they were please somebody finally caught up with their disk designs. Anyone remember 200MB Conner Chinook dual actuator HDDs?

      1. robidy

        Re: '90s Called...

        Next someome will come up with a technology that doesn't need any moving parts like RAM but remembers stuff when you have a power cut...

      2. Ian Baker

        Re: '90s Called...

        Yes - my immediate reaction was 'This has been done before'

        1. Slap

          Re: '90s Called...

          My immediate reaction was “Failure Rate?”

          1. DougS Silver badge

            Re: '90s Called...

            Failure rate shouldn't be an issue. The previous attempts at this technology replicated the entire set of read-write heads, so you had 2x as many things to go wrong. This simply divides the full set into two, one half can access half the drive, the other half can access the other half of the drive. The same number of read/write heads in total, two actuator mechanisms instead of one but each are smaller - meaning a bonus in terms of faster seek times.

            Basically if you had a 16TB drive with this technology it would perform like two slightly faster 8 TB drives.

      3. gordon123

        Re: '90s Called...

        Beat me to it (and - spookily - with a very similar name).

        Yes, Chinook was the internal name I believe for their high end drive that had two actuators - one at either end of the platter. A bit of a nightmare really as with it being a totally different head stack doing a similar job I think there might have been some tracking challenges.

        Add that to the much higher costs due to 2x head-stacks, and I guess we can see why it never took off.

        I like this idea of splitting the stack though. Not sure why nobody did this before. (Maybe they did..?)

        1. TechnicalBen Silver badge


          How much of this invention is just waiting for things* to me small enough or reliable enough to make it to consumers? Given enough time, would we not see each arm having it's own actuator? Then I guess it's onto solid state read/write magnet tracks (memresistor)?

          *for others to do the work or doing it themselves. ;)

          1. DougS Silver badge

            Re: Miniaturisation?

            This technology will NEVER come to consumer hard drives, because consumers are no longer the target market for leading edge hard drive development. Consumers are being sold old technology hard drives which will never get the latest technology because the market is too cheap, small and continually shrinking so it cannot justify R&D expenses.

            It wouldn't benefit consumer hard drives anyway, because consumers don't generate enough overlapping I/O 99.99% of the time for this to help. Those few who do generate overlapping I/O should buy an SSD.

            1. Naselus

              Re: Miniaturisation?

              I suspect he may have been using 'consumer' in the sense of 'end user' rather than 'home market'. But yes, there's not really any home user who's ever going to need this kind of performance - this is for NAS devices with hundreds or thousands of concurrent users, who are bottlenecking on drive performance. That's not really likely to occur in the home.

              Still doubt that we'll see every head given an individual actuator eventually, though; it's not that cheap an option and there's a serious diminishing return to the IOPS improvement as e=more heads become independent.

              1. DougS Silver badge

                Re: Miniaturisation?

                Why should there be any diminishing return in IOPS as you increase the number of heads? Due to the smaller size of the actuator meaning it can move slightly faster, you actually give slightly more than n * IOPS for n heads. Throughput increases exactly with n.

                This depends on the drive having enough I/O requests coming in to keep it busy, but that shouldn't be a problem for cloud providers where this is targeted at. It would make much less difference for consumer drives in a PC (which it will never be offered to) because their drives at idle almost all the time.

                The other advantage is that RAID rebuilds take place more quickly - n times faster based on n heads (exactly n since it is a sequential process)

                1. Naselus

                  Re: Miniaturisation?

                  "Why should there be any diminishing return in IOPS as you increase the number of heads?"

                  There's not a diminishing return in the IOPS (provided you're always running the disk at maximum). There's a diminishing return in the relative improvement you're seeing over the previous upgrade.

                  So if you have the traditional 1 fixed set, you have performance X, and spliutting the stack in half basically doubles your output to 2X ( plus a fairly negligible increase from weight reduction). That's a 100% performance improvement for the price of the additional actuators. But adding a third arm only takes you from 2X to 3X, so that's only a 50% improvement over the 2X.

      4. Peter 39

        Re: '90s Called...

        The 90's ... really ???

        No. This is a 1960's scheme, with giant platters and one head for each surface.

      5. RLWatkins

        Re: '90s Called...

        The '90s? Remember those washing machine-sized 20MB top-loading unsealed multi-platter drives that old DEC and DG boxes used? I recall some DEC guys experimenting with putting four sets of actuators and heads in those in the mid 1970s.

        Cool idea, and interesting trying to come up with software which would take a read/write queue and optimally route the requests to the appropriate heads... on a machine with a 64K address space, no less.

        This profession has always been a blast, and stays that way - as much fun as you can have with your pants on.

        1. Anonymous Coward
          Anonymous Coward

          Re: '90s Called...

          This profession has always been a blast, and stays that way - as much fun as you can have with your pants on.

          You still wear pants? That is why we telecommute....

    2. Blank Reg

      Not only performance improves, but rebuild time when one (or more) of your 10+GB drives fails in a RAID array are horrendous. Though power consumption and required space will be higher with all those tiny little drives.

  2. frank ly Silver badge

    Worth the effort?

    They seem to have packaged two physical drives in one physical unit. Maybe the on-board controller can also treat them both as one physical drive but isn't it more flexible and perhaps cheaper to concentrate on making a single physical hard drive robust and cheap and then use RAID and similar techniques to get performance increases?

    If you want to go this route, why not package an extra entire independent set of read/write heads at the opposite corner, then you could really have two channel access to the same physical drive?

    1. Anon

      Re: Worth the effort?

      I suggested the sets of heads on opposite corners a long time ago. Double the rate of read-after-write verification. Read an entire track in half the time. Zero adjacent track-to-track seek time. But would they listen? Noooo.

      1. Geoff Campbell

        Re: Worth the effort?

        Someone (Conner, perhaps?) did try such a thing. It didn't catch on.

        Realistically, we're in the end game for spinning rust now, so big new innovations seem a little pointless to me.


        1. Geoff Campbell

          Re: Worth the effort?

          Ah, yes, here we are:



          1. Peter2 Silver badge

            Re: Worth the effort?

            "Realistically, we're in the end game for spinning rust now, so big new innovations seem a little pointless to me."


            Personally, my storage is m2 SSD, PCIE SSD and a couple of large drives for keeping large amounts of data. I agree that SSD's are the future.

            However, i also think that given the production costs and capacity of memory for SSD's we will still have HDD's with us in 20 years time. Why?

            If your Dell/HP/Fijitsu/etc making a budget desktop, then what's it going to take to replace the HDD? A 500GB HDD can be had for £25 at retail prices. Large OEM's will get it cheaper than that. An SSD is over quadruple this price. The SSD will kill the HDD when the price reaches parity.

            That won't happen absent a new fabbing technology for memory chips that reduces the cost by around 400%. Ergo HDD's are going to hang around at the low end of the market for cheap drives, and for large scale storage where it can win in cost per GB over SSD.

            The "end game" for HDD's is sort of like the "end game" for tape. Yeah, it's going to get pushed into niche markets but it's going to survive there for decades, and some of those niche applications (like enterprise storage on SANS) are massively huge.

            1. Naselus

              Re: Worth the effort?

              "Yeah, it's going to get pushed into niche markets but it's going to survive there for decades, and some of those niche applications (like enterprise storage on SANS) are massively huge."

              Agreed. If you look beyond end-user storage (which most commentards apparently struggle to do) and look instead at worldwide storage requirements, it's clear that Flash remains a minority and is not expanding as quickly as data storage is. Flash may dominate your options at PC world, but it's not what big organizations are storing their petabytes of data on.

              I suspect that, long-term, NAND might be in more danger than spinning rust, simply because people are actively looking for something faster than flash and it's very expensive to produce (and even more expensive to produce the fabs to produce it). If something out-performs it, Flash suddenly becomes second-rate tech with a heavy price tag, and no new Flash foundries will be springing up to push that price down. On the other hand, the only reason I'd replace most of my slow-tier 7.2k disk is if something much cheaper appeared with the same performance - rather than something much more performant at the same price. No-one is really throwing much effort into finding that, since disk is already cheap.

              Flash has probably already eaten all the disk market that it's going to, basically wiping out the 15krpm and 10krpm classes completely. But the things Flash does well are not the things 7.2k rpm does well, and as a storage admin there's a lot of situations where I wouldn't even consider Flash as an option.

    2. Warm Braw Silver badge

      Re: Worth the effort?

      Or just go the whole hog?

  3. Doctor Syntax Silver badge

    Wouldn't an 8 platter drive need 16 heads or are they just using single sides these days?

    In effect this splits the drive into two logical drives. There needs to be a prize for someone who has the bright idea of using these as a mirror pair. A wooden spoon?

    1. AstroNutter

      Could use them as a stripe set.

      But then why didn't that do that already in the drive controller? Not like there's going to be any other advantages, other than two drives in the space of one. You still get the problem of one drive fails, both need replacing.

    2. John Robson Silver badge

      I need another wooden spoon for the kitchen...

      And this was my first thought.

      Why involve any change externally. With the size of drive caches nowadays the disk is doing all the data rearranging anyway, so it could reasonably intelligently divvy the data up itself.

      Of course a naive striped pair approach would simply tie the heads back together again (on write at least), but an internal firmware change to take advantage of what I suppose is effectively 'more spindles' strikes me as an easier approach than most other options (unless you genuinely present as two disks (can a normal SATA/SAS port take that?)

  4. Anonymous Coward
    Anonymous Coward

    What's the point?

    I can maybe see the point if you're a hyperscale cloud provider, but surely in this day and age if you need more IOPS on premises you're just using flash? I've even got plenty of customers using flash for bulk serial IO now as well because it's cheaper to run one type of disk than two.

    I just don't see where a disk that produces maybe 1.5-2x more IOPS for the same bandwidth fits into a modern architecture.

    1. Anonymous Coward
      Anonymous Coward

      Re: What's the point?

      > I just don't see where a disk that produces maybe 1.5-2x more IOPS for the same bandwidth fits into a modern architecture.

      It could be double the IOPS *and* double the bandwidth, as long as there are two sets of electronics which can read/write to both halves simultaneously. People who don't need the IOPS could use it as a RAID0.

      Having said that: I never understood why hard drives don't "stripe" across all heads. If you have 4K sector size (which is common in modern drives), and 8 heads, you could write a 512 byte chunk on each head simultaneously. You waste some capacity in inter-block gaps (which is what the 4K sector size was supposed to fix in the first place), but you get 8 times the throughput.

      1. really_adf

        Re: What's the point?

        Having said that: I never understood why hard drives don't "stripe" across all heads.

        AIUI head alignment requires constant adjustment so you can only have one head aligned at a time if they are mechanically linked. Unless, I guess, you massively reduce density and hence capacity.

        1. Dwarf Silver badge

          Re: What's the point?

          Having said that: I never understood why hard drives don't "stripe" across all heads.

          They do, its called a cylinder, you look down the heads across all surfaces and write across them,

          See CHS Hard Disk Addressing

          No reason to believe that the vendors stopped doing this when they moved the external interface to LBA back around 1980 ish

          Unlike what the other post on this thread claims, its not hard to analyse errors on a per surface perspective, since the drive's controller and firmware knows the real geometry of the drive and grown defects do just that, so you can easily determine if the failed sector is adjacent to an existing defect.

          None of this is new technology.

      2. DJO Silver badge

        Re: What's the point?

        Having said that: I never understood why hard drives don't "stripe" across all heads.

        Hard drive are not as infallible as you might think. They all have a overhead of capacity which can be brought into use if any sectors start to look a bit iffy, this is long before the SMART stuff kick in.

        If you striped across all platters a duff sector on one platter would effectively mean a duff sector on all platters which would eat the capacity too quickly.

      3. inmypjs Silver badge

        Re: What's the point?

        "why hard drives don't "stripe" across all heads"

        Because a head is servo positioned on the track it is reading or writing and the alignment between head and track on other platters is no where near good enough. For example at current densities a 1 degree C temperature differential between two aluminium disks would produce a thermal expansion differential about 6 tracks wide at 1 inch from the spindle.

        I would speculate micro (probably piezo) actuators on each arm could accommodate errors and allow one head on each arm to servo onto the 'same' track. Would need a lot more electronics to achieve.

  5. Alan Brown Silver badge

    about the only possible use that I can think of

    Is to have them seeking in equal but opposite directions so the torque moments cancel.

    Being able to read/write simultaneously on all heads would be more of an improvement (they're currently accessed sequentially)

    1. DougS Silver badge

      Re: about the only possible use that I can think of

      They can't read/write on multiple heads at once because the tracks are so close together that thermal variation means that all heads don't align with the same tracks every time. They'd have to reduce density by a fairly significant margin to do what you suggest.

      1. Alan Brown Silver badge

        Re: about the only possible use that I can think of

        I'm aware of why they don't work in parallel, nonetheless it would still be an improvement if they could.

        The next logical step from what this proposition is to move to an independent arm per platter (2 heads).

        Personally I don't think this will work well enough to leave the lab.

        Apart from the issue of conflicting magnetic fields on the other side of the pivot (ie the field driving one arm will perturb the other one), I suspect that turbulence issues will raise their ugly heads in short order. There's a lot of funky hydrodynamics at work keeping a hard drive's heads afloat and they tend to assume smooth airflow.

    2. DougS Silver badge

      Re: about the only possible use that I can think of

      Doubling bandwidth and IOPS isn't good enough, you think the only use is cancelling torque moments? Each mechanism would weigh only slightly more than half the weight of the full (current) mechanism, so even when they both swing the same way the torque is barely greater than it is now.

      What I wonder is whether the movement of the second set of heads will cause vibration that throws off the first set when it is actively reading and writing. It may require more vibration damping than current drives, but that's fine since this is not targeted at moving devices like laptops, and they can easily mandate specific mounting requirements that would be infeasible for consumer targeted PC drives.

  6. RockBurner

    isn't the logical conclusion to this for each individual disk to have 2 independant arms (one read, one write).

    Obviously you'd have 2 pivot posts (not impossible), with each arm operating independantly on the post (I suppose it depends exactly where the electric motor actuating the arm movement is located).

    the main challenge would be packaging it all up, rather than anything else.

    1. Aladdin Sane Silver badge

      The fluid dynamics would be interesting. Currently, heads 'fly' on a cushion of air generated by the spinning disk. If 2 pivot posts are in use, the heads might interfere with airflow and insufficient lift may cause head crash.

    2. DougS Silver badge

      No, separate arms for read and write would be far inferior to what they've done. This allows them to double read and write bandwidth (assuming you have enough I/O that each 'half' of the drive is fully utilized) and more than double IOPS. Yes, more than double, because you not only have two sets of heads, each accessing half the drive, but since each mechanism has half the heads it weighs less which means seek times are slightly faster.

  7. Prst. V.Jeltz Silver badge

    This is why all cars have 2 camshafts these days. Lightbulb moment.

    1. Unicornpiss Silver badge


      "This is why all cars have 2 camshafts these days. Lightbulb moment."

      Actually not nearly all cars have or need 2 camshafts. Including some quite powerful ones.

  8. Anonymous Coward
    Anonymous Coward

    Well that's novel. Or maybe not.

    See e.g. Conner Peripherals product codenamed "Chinook" (it's on Wikipedia).

    And long before Chinook there were things that can probably be found in places like Jim Austin's Computer Collection; standard (for the era) size disk drives that would fill a 19" rack or more, with multiple independently operatable disk heads. My memory is failing, I cannot quickly find any particular examples of such a product, but they did exist.

    1. RealBigAl

      Re: Well that's novel. Or maybe not.

      Have an upvote for Connor Peripherals. I remember them in some old Compaq machines.

    2. Alan Brown Silver badge

      Re: Well that's novel. Or maybe not.

      " with multiple independently operatable disk heads."

      There's a reason you don't see them anymore - and can't find museum examples. They were unreliable.

  9. ThaumaTechnician


    Here I was, looking at the image thinking: "Wow! They're using a set of write-only platters and another set of read-only platters? I'd like to see a graph of performance vs. cost..."

    /really, this is worth a headline?

    1. Norman Nescio Silver badge

      Re: Dang!

      Perhaps I'm missing something here, but wouldn't that graph would be a flat-line at zero? My thinking being, "How would the data get off the write-only platters, and data onto the read-only platters?".

      On reading the headline, I thought they had optimised one set of heads for reading and one set for writing and given them separate actuators, which couls have been interesting.

      1. ThaumaTechnician

        Re: Dang!

        How? The Signetics 25120 to the rescue.

  10. Alister Silver badge

    Make read/ write heads operate independently (on seperate platters)

    So, not actually, then.

  11. Daniel Hall

    I cant be the only one..

    ..that initially read the heading and thought, oh cool, one actuator for reading and another actuator positioned somewhere just for writing...


    1. Doctor Syntax Silver badge

      Re: I cant be the only one..

      Followed rapidly by "Wouldn't it be better to have them both read/write?" heads. And that followed by "That's what they've done". Followed in turn by "But they've only addressed half a cylinder at a time. Why didn't they make two separate arm sets and make them full height?".


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