4 ms·

Not much, actually. Dual actuators only improve parallelism, not media transfer rate or latency. In practice, dual actuators don't even double external transfer

Not much, actually. Dual actuators only improve parallelism, not media transfer rate or latency. In practice, dual actuators don't even double external transfer rates due to occasional latency (which is unavoidable even for the best-case scenarios) and internal contention elsewhere in the drive. Even if you had four actuators working perfectly in concert, and weren't bottlenecked on the external interface speed (which you would be), a 4x improvement in transfer rate vs. a 8x increase in capacity would still mean a 2x increase in fill/empty time. As with the shift from 5.25" to 3.5" to 2.5" and even 1.8" drives, the only way out of this bind is really to take advantage of the improved areal density to make drives that are the same capacity but smaller and pack more of those into the same volume or power/heat envelope. Drive manufacturers could help this along a little bit e.g. by sharing a motor and some environmental bits between what are otherwise completely separate drives (including separate external interfaces) within a single package, but mostly we'd all better get used to higher drive counts. Dual actuators - and this is far from the first time they've been tried BTW - are mostly a red herring. Background: I worked on exactly these problems for the latter half of a thirty-year career, most relevantly at my last job working on an exabyte-scale storage system at a FAANG.

effie 6y ago
Interesting. What do you think about Seagate's claim that dual actuator decreases their costs because it takes less time to test the drive? Is that the real reason for dual actuator?
PaulHoule 6y ago
Also what market is there for big hard drives outside of FAANG and a few other places? Retailers in my area (e.g. Best Buy) don't stock hard drives larger than 4 TB; I was going to tell somebody who lived in the Valley that he's lucky to be able to go to Fry's and then Fry's closed down. Those same retailers stock both budget and quality SSD's up to 2TB in size. Most upgraders and the system builders are happy. For the rest of us there is Amazon where the Seagate Exos "enterprise" drive costs half of what similar "consumer" drives cost, has a great reputation and does not seem hard to live with at home. I would not take it for granted at all that a backup, RAID rebuild, restore, metadata scan or any full scan would work on such a disk if I hadn't tested it -- it is just that kind of technology. Synology is not crazy at all when they make you buy branded large drives to go in the enclosure.
- notacoward 6y ago
  > what market is there for big hard drives outside of FAANG and a few other places? I wouldn't consider myself an expert on market numbers, but I'd say you generally shouldn't be using the larger drives. As others have said, disk is the new tape. Unless you have the kind of system where you might once have used tape - i.e. one with a substantial ice-cold-data component - larger disks are likely to be an ill fit. Even where they are a good choice, that's mostly going to be in a tiered architecture with flash etc. to suck all the "heat" out of the data going into them.
  - cbozeman 6y ago
    And what exactly are people going to use? I can get a used server on eBay with 96 TB of storage, usually in 12 x 8TB configs for around $2000 - $2500. Flash drives? I'll spend 10 times that... hell, probably more. I love having my movies, music, television, etc. on my home server, but I don't love it at the level of 25 large. Now $2500? That's a lot more reasonable.
    - notacoward 6y ago
      Sounds like you have a solution that works with today's medium-sized drives, so how is this even relevant to a discussion of 60-120TB drives? Do you think you'd be well served by putting that 96TB on one drive? I doubt it. If your active set (for any useful or relevant definition of "active") is X and the number of drives you need for IOPS or MB/s is Y, then the ceiling for how much you can effectively use per drive is X/Y. That's quite likely less than current drive capacities, and almost certainly within what can be achieved by current PMR technology. How would HAMR or BPM or any other more fundamentally new disk technology actually help you other than to store cold data on that "spare" capacity?
      - Robotbeat 6y ago
        Yes? I mean, the sequential write speeds are fine for many video-heavy applications. You don’t want it in cold storage. Tape drives are not cheap. And neither is retrieving from tape terribly practical, either. There’s a large overhead for tape storage if you want it automatically accessible (ie a big tape jukebox). A big hard drive can store large volumes of data just a few milliseconds away, not minutes as you have to wind the tape to the right spot in a big tape jukebox... or hours or days if you have to ask someone to retrieve some tapes by hand. And can do hard drive storage for an order of magnitude lower cost than SSD. Spinning disk is still really useful for video. Which is not shrinking any time soon.

effie 6y ago

Interesting. What do you think about Seagate's claim that dual actuator decreases their costs because it takes less time to test the drive? Is that the real reason for dual actuator?

PaulHoule 6y ago

Also what market is there for big hard drives outside of FAANG and a few other places? Retailers in my area (e.g. Best Buy) don't stock hard drives larger than 4 TB; I was going to tell somebody who lived in the Valley that he's lucky to be able to go to Fry's and then Fry's closed down. Those same retailers stock both budget and quality SSD's up to 2TB in size. Most upgraders and the system builders are happy. For the rest of us there is Amazon where the Seagate Exos "enterprise" drive costs half of what similar "consumer" drives cost, has a great reputation and does not seem hard to live with at home. I would not take it for granted at all that a backup, RAID rebuild, restore, metadata scan or any full scan would work on such a disk if I hadn't tested it -- it is just that kind of technology. Synology is not crazy at all when they make you buy branded large drives to go in the enclosure.

notacoward 6y ago
> what market is there for big hard drives outside of FAANG and a few other places? I wouldn't consider myself an expert on market numbers, but I'd say you generally shouldn't be using the larger drives. As others have said, disk is the new tape. Unless you have the kind of system where you might once have used tape - i.e. one with a substantial ice-cold-data component - larger disks are likely to be an ill fit. Even where they are a good choice, that's mostly going to be in a tiered architecture with flash etc. to suck all the "heat" out of the data going into them.
- cbozeman 6y ago
  And what exactly are people going to use? I can get a used server on eBay with 96 TB of storage, usually in 12 x 8TB configs for around $2000 - $2500. Flash drives? I'll spend 10 times that... hell, probably more. I love having my movies, music, television, etc. on my home server, but I don't love it at the level of 25 large. Now $2500? That's a lot more reasonable.
  - notacoward 6y ago
    Sounds like you have a solution that works with today's medium-sized drives, so how is this even relevant to a discussion of 60-120TB drives? Do you think you'd be well served by putting that 96TB on one drive? I doubt it. If your active set (for any useful or relevant definition of "active") is X and the number of drives you need for IOPS or MB/s is Y, then the ceiling for how much you can effectively use per drive is X/Y. That's quite likely less than current drive capacities, and almost certainly within what can be achieved by current PMR technology. How would HAMR or BPM or any other more fundamentally new disk technology actually help you other than to store cold data on that "spare" capacity?
    - Robotbeat 6y ago
      Yes? I mean, the sequential write speeds are fine for many video-heavy applications. You don’t want it in cold storage. Tape drives are not cheap. And neither is retrieving from tape terribly practical, either. There’s a large overhead for tape storage if you want it automatically accessible (ie a big tape jukebox). A big hard drive can store large volumes of data just a few milliseconds away, not minutes as you have to wind the tape to the right spot in a big tape jukebox... or hours or days if you have to ask someone to retrieve some tapes by hand. And can do hard drive storage for an order of magnitude lower cost than SSD. Spinning disk is still really useful for video. Which is not shrinking any time soon.