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Future Seagate HDDs will begin including two separate sets of actuator arms that can operate independently in order to double read/write speeds:
Seagate's multi-actuator technology is a simple concept, and the idea certainly isn't new. In fact, the company has already developed drives with multiple actuators in the past, but they weren't economically viable due to higher component costs.
Most HDDs read and write data to and from multiple platters. For instance, Seagate's largest drives wield up to 8 platters and 16 heads. The heads, which are connected to the end of an actuator arm assembly, read and write data from both sides of each platter.
Unfortunately, those 16 heads are all aligned on the same arm, which means they all move in unison. Simultaneously aligning all the heads on all the platters isn't possible because of the incredibly thin data tracks on the platters, so only one of the heads is actively reading or writing data at any given time. That limits read/write throughput and performance with randomly accessed data.
Seagate's new design uses two sets of actuator arms that operate independently. Each carries eight heads. That means the drive can read or write from two heads at once, provided they are attached to different actuator arms. The drive can respond to two commands in parallel and one head can read while another writes, or both can read or write simultaneously.
(Score: 1, Interesting) by Anonymous Coward on Wednesday December 20 2017, @10:22AM (10 children)
Let us double the number of parts to fail!
Honestly, double actuators for the same track would make more sense. That way if you started having a head failure with one, you have a backup to offload your data before the drive fails completely.
This way, you just have more of a chance of losing half the drive, and most likely interleaved cylinders/sectors/tracks if it provides a throughput boost.
New hardware designs are definitely not always better than old ones.
(Score: 0) by Anonymous Coward on Wednesday December 20 2017, @10:46AM (1 child)
You make a good point that it /could/ lead to longer living drives on top of the better througput. Unfortunately I can't help but see this as a late in the game attempt by Seagate to remain relevant. If you care about perfoance in a drive you're likely picking a Samsung or Intel SSD over the lackluster Seagate hybrids.
This tech is seriously old. It was once used with 2 separate interfaces so you could deliver content to webservers through read-only arms. Pretty sure that died a quick death.
Conspiracy theory - "BONUS" they could set the SMART data however they like so you are only warned about a bad read/write element outside of warranty, as the failure can remain "hidden" for longer. **yay Seagate**
(Score: 3, Informative) by takyon on Wednesday December 20 2017, @02:46PM
Not sure I would tie this so closely to Seagate. Once Seagate does something, WD is sure to follow, and vice versa. Even Toshiba still has skin in the game, miraculously.
WD/HGST moved to helium-filled drives, Seagate followed, and later Toshiba [anandtech.com]. Both companies had been working on it for years.
All three companies have moved past 5 platters and back into the territory of 7-9 platters. We could see 12 platters on a glass substrate [soylentnews.org] in 3.5".
Seagate is moving to HAMR, WD is moving to MAMR, which is similar.
Seagate is using shingles (although not in all drives), even with its disadvantages, and so is WD [storagereview.com].
Both companies are working on two-dimensional magnetic recording (TDMR), which should boost capacity by a few percent.
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 0) by Anonymous Coward on Wednesday December 20 2017, @10:48AM (1 child)
If I understand the concept correctly, each individually operated actuator + set of heads can cover the entire drive surface anyway, which covers your scenario of a single head failure. If anything, if designed correctly, I see doubling of parts as creating redundancy inside the drive, not adding more single points of failure. The additional read/write throughput is a bonus. If you lose a head on today's drives, you lose access to the data on what, once side of an entire platter? This design fixes that issue. Not that I'm sure if it's even a common failure case.
(Score: 5, Informative) by WizardFusion on Wednesday December 20 2017, @10:59AM
Not according to the animation.
One actuator arm covers the top half of the platters, and the other arm covers the bottom half. If you lose a head, you still lose access to the platter.
(Score: 3, Interesting) by shrewdsheep on Wednesday December 20 2017, @02:35PM
OTOH the force needed to move each arm is halving (or so). So maybe that is a good thing.
(Score: 2) by frojack on Wednesday December 20 2017, @07:07PM (2 children)
The source of the underlying problem was mentioned:
It almost leads one to believe the tracks are there on the drive before the build it.
I thought those things were laid down as needed, and the system remembered just how far to move the arm to find it again.
It would seem that you could always seek to a given physical track and create other tracks would align under the other heads.
These x tracks could be read and written in parallel.
The system would then only need to remember that when you wanted track 342, you need to seek head one to 338, and then read with head 5 (as an example), but also with heads 1-n would also be aligned on tracks that were logically (but not necessarily physically) consecutive tracks, and could be accessed in parallel.
No, you are mistaken. I've always had this sig.
(Score: 2) by bob_super on Wednesday December 20 2017, @07:23PM
> when you wanted track 342, you need to seek head one to 338, and then read with head 5
When you need to read from track 342, go to track 342 and read/write using all 8 to 16 heads, with the data split between platters, multiplying throughput. Bit interleave gives the fastest latency to first word, but byte or word interleaves would still provide the benefit.
(Score: 0) by Anonymous Coward on Thursday December 21 2017, @02:44PM
I always assumed the arms/heads laid down the tracks and that's why you can't have different heads on different arms serving the same track. Their opinions on where track #12 is would be different enough to not work well...
(Score: 2) by Immerman on Wednesday January 10 2018, @03:32PM (1 child)
How common is head failure as a cause of drive failure though? I tend to use drives to destruction, and almost all of them have failed in the "rapidly expanding regions of bad sectors" typical of surface failure. The remainder simply became completely non-responsive, disappearing even from the BIOS, which I assume indicates control board failure.
Not once have I seen the "regular stripes of unreadable data" that I would assume would be characteristic of a failed head.
That said, I would love to see multiple arms per platter for performance reasons, seems like you should be able to fit at least a few around the platters without even redesigning them.
The performance benefits of this seem... dubious, despite their in-house benchmark claims. It is after all effectively two mostly independent half-size drives sharing the same spindle and control board - and by it's nature each arm will have only half the throughput of a single integrated arm. So linear I/Os will have, at best, the same speed as they would with a single arm, while random I/O will only benefit if successive accesses fall on opposite semi-drives. A deep enough command queue should make that feasible to arrange, but I'm not sure how typical that demand would be.
Really, I can't see any way they'd see anything close to 2x the performance in real-world benchmarks unless they were comparing it to a drive with only half the number of platters.
(Score: 2) by Immerman on Wednesday January 10 2018, @03:41PM
Wait. Never mind, I missed:
> Simultaneously aligning all the heads on all the platters isn't possible because of the incredibly thin data tracks on the platters
I always assumed all the heads operated simultaneously so that you could read/write an entire cylinder at once. If you're only using one head at a time, then yeah, being able to use two heads at a time would double your throughput even for linear I/Os.