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This is cool, but I really need to hear more about how I can effectively use these kinds of drives in storage pools and backup applications without issue. I di

This is cool, but I really need to hear more about how I can effectively use these kinds of drives in storage pools and backup applications without issue. I didn’t have time to learn back when the first disaster hit with SMR drives got snuck in without warning and we had a small outrage event. I’m happy for new drive tech but I’ve not seen much about the pros and cons of HAMR in real world use yet. Which could be because there’s no difference from traditional Perpendicular Magnetic Recording (PMR) hard drives, but then again it could have its own subtle set of trade offs entirely different to the ones that Shingled Magnetic Recording (SMR) drives do.

jiggawatts 3y ago
From what I’ve heard, these are primarily sold to the hyperscalers like the public clouds, Drop Box, etc… At their scale it’s easy to utilise these efficiently despite the limitations. They’re not very good in a small NAS or disk array. You’d need a big write cache in front of them and an OS that natively understands the sector groupings.
- techdragon 3y ago
  This is why I’m looking for more info. This is talking about how they are already sending these out to Hyperscale customers, and they will eventually be in individual customers hands… so it would be good to know what file systems and cache setups are needed in order to benefit from this. I used to just rely on FreeNAS but it’s not as straightforward anymore. I’m having to consider Linux and looking at bCache FS and ZFS vs BTRFS and how all this compares on an all PCIe (m.2) flash drive setup… where a drive (or two) at this sort of size (~50TB) would make a great second backup copy of the flash array that can be started and stopped to periodically make the backups to save power… but then you have to think about copy efficiency since I don’t want to have them wasting read bandwidth from the flash drives… and the best is usually like to like file system copy ZFS -> ZFS and BTRFS -> BTRFS … so it adds another complication into a mix that is already far from simple. So it’s become something I’m keeping an eye out for… hopefully before it becomes something I may purchase, someone will have already done a good writeup.
  - wtallis 3y ago
    The simple answer is that the software stack necessary for consumers to effectively use these storage devices does not yet exist. Hyperscalers are pretty much defined as the ones who are big enough to do their own software stack. For the rest of us, we have some good components to work with but also some major gaps that won't be filled anytime soon. ZFS is a great improvement over traditional hardware RAID systems, but is still in many ways clearly a descendant of them. BTRFS has a slightly different mix of features from ZFS that make it a bit more flexible and a better choice for consumers who don't buy drives by the dozen. Neither has a great solution for caching/tiering with SSDs and hard drives. Ceph has a lot of features that would otherwise be almost exclusive to the hyperscalers, but is too complicated for something like a turnkey NAS. bcachefs aspires to eventually have most of the features you would want for a non-clustered storage system. Zoned storage is something many of the above already have some degree of support for, but as a paradigm it has not even started showing up in the consumer computing ecosystem so many of the issues with adopting zoned storage for consumer systems aren't even being worked on.
    - XorNot 3y ago
      ZFS has the concept of a separate intent log device though, I wonder if that would be enough to make these types of disks work with it? I have no problem putting a couple of terabytes of flash in front of a ZFS array if it means I can have 40TB of redundant storage in 3 disks.
      - wtallis 3y ago
        The ZFS intent log is an example of a supremely disappointing, underwhelming way to integrate SSD storage into your system. Fundamentally, it's just a workaround for the fact that most of the write caches preexisting in the storage stack are volatile caches and thus not safe. Putting the ZIL on an SSD allows you to get the safety without sacrificing the performance benefits of the write caching (performance that everyone has come to rely on). But the ZIL doesn't help with read performance, and the data you write to it is never even read unless you have a crash or power failure. And then for the read caching, ZFS has L2ARC as an entirely separate feature. So ZFS does technically have ways to take advantage of SSDs to improve a hard drive storage array—but I don't think anyone would consider it to be an ideal solution, more of a pragmatic minimum viable feature.
- crabbone 3y ago
  Big disks present a problem in the cloud provider environment: users typically want to partition them into smaller logical disks... but this means that larger disks must also have lower latency / higher bandwidth to service multiple users at the same time. Most likely, cloud vendors have a large choice of sizes to try to match requested sizes of logical disks to physical disks, but if most users don't want / need disks that are this big (or bigger), then the provider will have a problem.
  - bombcar 3y ago
    Big disks have their place; both as selling "large bulk storage" to cloud users (most cloud systems use SSD as the "main/OS" drive now anyway) but also as near line backup storage.
pclmulqdq 3y ago
I am not entirely sure that HAMR will be too different from CMR/PMR drives. The premise of HAMR is that they heat the area under the head, expanding it, for reads and writes, and otherwise they are essentially CMR devices. This isn't like SMR, which had huge implications for drivers (due to the overlap in the bit lines). There must be a significant durability cost to HAMR, but I don't think the difference in drivers will be nearly as big for HAMR as it was for SMR.
- robotnikman 3y ago
  I'm guessing then that they will probably use a little bit more power then, but otherwise similar to CMR/PMR in performance. That heated head element though seems like a massive point of failure, though I have no idea how durable the technology it.
  - dgacmu 3y ago
    The heating is done by a solid state laser diode. It should be very reliable other than adding one more thing to an already complex drive head. (Which undoubtedly means the first generation or two will have some kinks to work out, but that's not a fundamental decrease, just engineering). And there shouldn't be much of an impact on durability. The heating is very brief - a nanosecond or so. The idea is not to expand the material physically, it's to increase its magnetic permeability temporarily so that you can write the bit to it and then it becomes stable again.
- rainbowzootsuit 3y ago
  The nanoscale heating manipulates the magnetic coercivity of the platter coating to allow the magnetic polarization to be manipulated. It seems somewhat analogous to modern day Magneto Optical but much finer scale and the readout is via a magnetic signal vs MO using an optical readout.
deleted 3y ago
[deleted]

jiggawatts 3y ago

From what I’ve heard, these are primarily sold to the hyperscalers like the public clouds, Drop Box, etc… At their scale it’s easy to utilise these efficiently despite the limitations. They’re not very good in a small NAS or disk array. You’d need a big write cache in front of them and an OS that natively understands the sector groupings.

techdragon 3y ago
This is why I’m looking for more info. This is talking about how they are already sending these out to Hyperscale customers, and they will eventually be in individual customers hands… so it would be good to know what file systems and cache setups are needed in order to benefit from this. I used to just rely on FreeNAS but it’s not as straightforward anymore. I’m having to consider Linux and looking at bCache FS and ZFS vs BTRFS and how all this compares on an all PCIe (m.2) flash drive setup… where a drive (or two) at this sort of size (~50TB) would make a great second backup copy of the flash array that can be started and stopped to periodically make the backups to save power… but then you have to think about copy efficiency since I don’t want to have them wasting read bandwidth from the flash drives… and the best is usually like to like file system copy ZFS -> ZFS and BTRFS -> BTRFS … so it adds another complication into a mix that is already far from simple. So it’s become something I’m keeping an eye out for… hopefully before it becomes something I may purchase, someone will have already done a good writeup.
- wtallis 3y ago
  The simple answer is that the software stack necessary for consumers to effectively use these storage devices does not yet exist. Hyperscalers are pretty much defined as the ones who are big enough to do their own software stack. For the rest of us, we have some good components to work with but also some major gaps that won't be filled anytime soon. ZFS is a great improvement over traditional hardware RAID systems, but is still in many ways clearly a descendant of them. BTRFS has a slightly different mix of features from ZFS that make it a bit more flexible and a better choice for consumers who don't buy drives by the dozen. Neither has a great solution for caching/tiering with SSDs and hard drives. Ceph has a lot of features that would otherwise be almost exclusive to the hyperscalers, but is too complicated for something like a turnkey NAS. bcachefs aspires to eventually have most of the features you would want for a non-clustered storage system. Zoned storage is something many of the above already have some degree of support for, but as a paradigm it has not even started showing up in the consumer computing ecosystem so many of the issues with adopting zoned storage for consumer systems aren't even being worked on.
  - XorNot 3y ago
    ZFS has the concept of a separate intent log device though, I wonder if that would be enough to make these types of disks work with it? I have no problem putting a couple of terabytes of flash in front of a ZFS array if it means I can have 40TB of redundant storage in 3 disks.
    - wtallis 3y ago
      The ZFS intent log is an example of a supremely disappointing, underwhelming way to integrate SSD storage into your system. Fundamentally, it's just a workaround for the fact that most of the write caches preexisting in the storage stack are volatile caches and thus not safe. Putting the ZIL on an SSD allows you to get the safety without sacrificing the performance benefits of the write caching (performance that everyone has come to rely on). But the ZIL doesn't help with read performance, and the data you write to it is never even read unless you have a crash or power failure. And then for the read caching, ZFS has L2ARC as an entirely separate feature. So ZFS does technically have ways to take advantage of SSDs to improve a hard drive storage array—but I don't think anyone would consider it to be an ideal solution, more of a pragmatic minimum viable feature.
crabbone 3y ago
Big disks present a problem in the cloud provider environment: users typically want to partition them into smaller logical disks... but this means that larger disks must also have lower latency / higher bandwidth to service multiple users at the same time. Most likely, cloud vendors have a large choice of sizes to try to match requested sizes of logical disks to physical disks, but if most users don't want / need disks that are this big (or bigger), then the provider will have a problem.
- bombcar 3y ago
  Big disks have their place; both as selling "large bulk storage" to cloud users (most cloud systems use SSD as the "main/OS" drive now anyway) but also as near line backup storage.

pclmulqdq 3y ago

I am not entirely sure that HAMR will be too different from CMR/PMR drives. The premise of HAMR is that they heat the area under the head, expanding it, for reads and writes, and otherwise they are essentially CMR devices. This isn't like SMR, which had huge implications for drivers (due to the overlap in the bit lines). There must be a significant durability cost to HAMR, but I don't think the difference in drivers will be nearly as big for HAMR as it was for SMR.

robotnikman 3y ago
I'm guessing then that they will probably use a little bit more power then, but otherwise similar to CMR/PMR in performance. That heated head element though seems like a massive point of failure, though I have no idea how durable the technology it.
- dgacmu 3y ago
  The heating is done by a solid state laser diode. It should be very reliable other than adding one more thing to an already complex drive head. (Which undoubtedly means the first generation or two will have some kinks to work out, but that's not a fundamental decrease, just engineering). And there shouldn't be much of an impact on durability. The heating is very brief - a nanosecond or so. The idea is not to expand the material physically, it's to increase its magnetic permeability temporarily so that you can write the bit to it and then it becomes stable again.
rainbowzootsuit 3y ago
The nanoscale heating manipulates the magnetic coercivity of the platter coating to allow the magnetic polarization to be manipulated. It seems somewhat analogous to modern day Magneto Optical but much finer scale and the readout is via a magnetic signal vs MO using an optical readout.

deleted 3y ago

[deleted]