4 ms·

SMR and zoned storage offer compete and total utter crap performance in the real world. They have all the glass jaws of early flash firmware (garbage collectio

by bcrl 3y ago

SMR and zoned storage offer compete and total utter crap performance in the real world. They have all the glass jaws of early flash firmware (garbage collection that took seconds to complete during which time no additional I/Os completed) while running on a medium that has many orders of magnitude higher latency than flash. Take 2008 era USB flash drives and that's about what you'll get out of an SMR HDD when using a write workload that isn't 100% large sequential writes. SMR might have become more relevant if it had provided a useful increase in density, but that never materialized as was originally promised. Retail prices for SMR drives were never much better than CMR. The largest generally available HDDs are available in CMR flavours because that's what's needed in real world servers. There's no 10x density improvement (or even 2x). Meanwhile flash is marching relentlessly down the cost reduction path afford by Moore's law + 3D layer stacking. Really fast 1TB NVMe SSDs are under $100 now, and it doesn't look like flash cost reduction is going to slow down any time soon.

rektide 3y ago
I wasn't really talking about SMR though, just some protocols they had that are now being re-used. I'm talking about Zoned Namespace SSDs (ZNS). Let's go back in time almost a decade. A bunch of smart people had figured out that the cumbersome Flash Translation Layer (FTL) on SSDs made it really hard to get expectable & consistent performance. They were building possible specs to try to directly access each flash block, to be able to fill them up as they saw fit & clear them out as they saw fit. They wanted direct access, with far less work juggling complex data-mappings done on the SSD itself. Two examples of Open Channel SSD works: https://openchannelssd.readthedocs.io/en/latest/ https://openchannelssd.readthedocs.io/en/latest/ http://lightnvm.io/ http://lightnvm.io/ Note the huge banner on the second: "Zoned Namespace (ZNS) SSDs have replaced the work on OCSSDs, and is now a standardized interface." Everyone realized that the protocols we had for Zoned Storage were basically adequate to get us what we wanted. We'd just make a lot of 128kB or whatever sized zones on the SSD, and let people manage them themselves. Currently this means opening blocks & then appending to them. There's been outstanding hope, in the future, that we might go further and allow more random write patterns, but still with the same contract of no over-writes (just clears). That work seemed like it was ready to go in 2020 & 2021. SSDs were supposedly sampling/becoming available. https://blog.westerndigital.com/zns-ssd-ultrastar-dc-zn540-sampling/ https://blog.westerndigital.com/zns-ssd-ultrastar-dc-zn540-s... https://semiconductor.samsung.com/newsroom/news/samsung-introduces-its-first-zns-ssd-with-maximized-user-capacity-and-enhanced-lifespan/ https://semiconductor.samsung.com/newsroom/news/samsung-intr... And that was reaffirmed again a year latter. https://www.tomshardware.com/news/samsung-and-western-digital-team-up-for-zns-ssds https://www.tomshardware.com/news/samsung-and-western-digita... But here we are in 2023 & there's still no Zoned Namespace SSDs (ZNS) one can purchase.
- wtallis 3y ago
  You can purchase them, just not from retailers. These drive break compatibility in annoying ways (eg. cannot boot a system off one), so it's totally reasonable that drive vendors would not be offering them through channels where unsuspecting customers could so easily buy something they cannot use.
  - Dylan16807 3y ago
    They didn't need to completely remove compatibility modes. And I'm not asking to get one off a shelf but not only can I not buy one on amazon or newegg I can't even find a price when I look for a specific model! I think it's fair to say that to a first approximation I, as a person, can't get one. Edit: I found one site with a price on a WD drive, but they only have refurbished drives and the price is 25% off of $2200 for 1TB, so I'm going to ignore that site.
    - wtallis 3y ago
      > I can't even find a price when I look for a specific model! That's true of most enterprise/server components. At most you'll find a laughably inflated list price that hardly anyone actually pays.
    - rektide 3y ago
      I really wouldn't mind buying special purpose hardware. In fact, I think I prefer it. The whole story here is that modern SSD controllers tend to embed a bunch of very fast very expensive data-processing cores to quickly do a ton of fancy mapping. We don't hear it quite as clearly these days, but for example for a while higher end Samsung SSD controllers were announced as penta-core ARM Cortex-R[1] systems, and I think those Cortex-Rs are what most folks do. (It was groundbreaking news that WD released an open source "swerv" RISC-V core which they'd experimented with using instead, https://blog.westerndigital.com/risc-v-swerv-core-open-source/ https://blog.westerndigital.com/risc-v-swerv-core-open-sourc... .) Ideally, the fantasy is, we can build much cheaper & faster controllers that do far less. Zoned Namespace drives should ideally have enterprise grade, fast, dual-port access, but in many ways, I feel like they should ideally be far cheaper than DRAM-less drives. They should leave even more up to the host. They should be incredibly dumb & simple drives. They should be lower power, by far. They should eskew DRAM. Drop all the legacy baggage & expose what you are, un-intermediated, so we can be fast & use it well. Which you, the drive, with all purpose tasks, could never do. It's not worth it, to me, to make a drive that still keeps the ancillary old baggage of convention. If you want to make a good ZNS drive, make a good ZNS drive. [1] https://en.wikipedia.org/wiki/ARM_Cortex-R https://en.wikipedia.org/wiki/ARM_Cortex-R
tremon 3y ago
SMR and zoned storage offer compete and total utter crap performance in the real world Yes, that's because we're in the drive-managed transition phase of zoned storage (not clear when -if ever- we'll leave that phase). The first zoned disks needed to present themselves as a dumb unit to the OS, because none of the operating systems had any support for it. Now that at least some OS'es have native support for zoned storage, we might finally see host-managed zoned storage on the market, but as you say -- the technology has not delivered on the projected storage benefits, so the value-add of CMR disks is very much an open question. And there's also the consumer confusion angle: how to market a device that can physically connect to their computer, but might logically not work at all? So I'd suspect to see the first host-managed drives in enterprise datacenters (think Amazon Glacier) -- but FAFAIK they're nowhere to be found.
- tremon 3y ago
  the value-add of CMR disks Argh. SMR, that is.

by bcrl 3y ago

rektide 3y ago

I wasn't really talking about SMR though, just some protocols they had that are now being re-used. I'm talking about Zoned Namespace SSDs (ZNS). Let's go back in time almost a decade. A bunch of smart people had figured out that the cumbersome Flash Translation Layer (FTL) on SSDs made it really hard to get expectable & consistent performance. They were building possible specs to try to directly access each flash block, to be able to fill them up as they saw fit & clear them out as they saw fit. They wanted direct access, with far less work juggling complex data-mappings done on the SSD itself. Two examples of Open Channel SSD works: https://openchannelssd.readthedocs.io/en/latest/ https://openchannelssd.readthedocs.io/en/latest/ http://lightnvm.io/ http://lightnvm.io/ Note the huge banner on the second: "Zoned Namespace (ZNS) SSDs have replaced the work on OCSSDs, and is now a standardized interface." Everyone realized that the protocols we had for Zoned Storage were basically adequate to get us what we wanted. We'd just make a lot of 128kB or whatever sized zones on the SSD, and let people manage them themselves. Currently this means opening blocks & then appending to them. There's been outstanding hope, in the future, that we might go further and allow more random write patterns, but still with the same contract of no over-writes (just clears). That work seemed like it was ready to go in 2020 & 2021. SSDs were supposedly sampling/becoming available. https://blog.westerndigital.com/zns-ssd-ultrastar-dc-zn540-sampling/ https://blog.westerndigital.com/zns-ssd-ultrastar-dc-zn540-s... https://semiconductor.samsung.com/newsroom/news/samsung-introduces-its-first-zns-ssd-with-maximized-user-capacity-and-enhanced-lifespan/ https://semiconductor.samsung.com/newsroom/news/samsung-intr... And that was reaffirmed again a year latter. https://www.tomshardware.com/news/samsung-and-western-digital-team-up-for-zns-ssds https://www.tomshardware.com/news/samsung-and-western-digita... But here we are in 2023 & there's still no Zoned Namespace SSDs (ZNS) one can purchase.

wtallis 3y ago
You can purchase them, just not from retailers. These drive break compatibility in annoying ways (eg. cannot boot a system off one), so it's totally reasonable that drive vendors would not be offering them through channels where unsuspecting customers could so easily buy something they cannot use.
- Dylan16807 3y ago
  They didn't need to completely remove compatibility modes. And I'm not asking to get one off a shelf but not only can I not buy one on amazon or newegg I can't even find a price when I look for a specific model! I think it's fair to say that to a first approximation I, as a person, can't get one. Edit: I found one site with a price on a WD drive, but they only have refurbished drives and the price is 25% off of $2200 for 1TB, so I'm going to ignore that site.
  - wtallis 3y ago
    > I can't even find a price when I look for a specific model! That's true of most enterprise/server components. At most you'll find a laughably inflated list price that hardly anyone actually pays.
  - rektide 3y ago
    I really wouldn't mind buying special purpose hardware. In fact, I think I prefer it. The whole story here is that modern SSD controllers tend to embed a bunch of very fast very expensive data-processing cores to quickly do a ton of fancy mapping. We don't hear it quite as clearly these days, but for example for a while higher end Samsung SSD controllers were announced as penta-core ARM Cortex-R[1] systems, and I think those Cortex-Rs are what most folks do. (It was groundbreaking news that WD released an open source "swerv" RISC-V core which they'd experimented with using instead, https://blog.westerndigital.com/risc-v-swerv-core-open-source/ https://blog.westerndigital.com/risc-v-swerv-core-open-sourc... .) Ideally, the fantasy is, we can build much cheaper & faster controllers that do far less. Zoned Namespace drives should ideally have enterprise grade, fast, dual-port access, but in many ways, I feel like they should ideally be far cheaper than DRAM-less drives. They should leave even more up to the host. They should be incredibly dumb & simple drives. They should be lower power, by far. They should eskew DRAM. Drop all the legacy baggage & expose what you are, un-intermediated, so we can be fast & use it well. Which you, the drive, with all purpose tasks, could never do. It's not worth it, to me, to make a drive that still keeps the ancillary old baggage of convention. If you want to make a good ZNS drive, make a good ZNS drive. [1] https://en.wikipedia.org/wiki/ARM_Cortex-R https://en.wikipedia.org/wiki/ARM_Cortex-R

tremon 3y ago

SMR and zoned storage offer compete and total utter crap performance in the real world Yes, that's because we're in the drive-managed transition phase of zoned storage (not clear when -if ever- we'll leave that phase). The first zoned disks needed to present themselves as a dumb unit to the OS, because none of the operating systems had any support for it. Now that at least some OS'es have native support for zoned storage, we might finally see host-managed zoned storage on the market, but as you say -- the technology has not delivered on the projected storage benefits, so the value-add of CMR disks is very much an open question. And there's also the consumer confusion angle: how to market a device that can physically connect to their computer, but might logically not work at all? So I'd suspect to see the first host-managed drives in enterprise datacenters (think Amazon Glacier) -- but FAFAIK they're nowhere to be found.

tremon 3y ago
the value-add of CMR disks Argh. SMR, that is.