How to Enable NVMe Zoned Namespaces

Hardware changes for ZNS

At a high level, in order to enable ZNS, most drives on the market only require a firmware update. ZNS doesn't put any new requirements on SSD controllers or other hardware components; this feature can be implemented for existing drives with firmware changes alone.

The critical element in hardware comes down to when an SSD is designed to support only zoned namespaces. First and foremost, a ZNS-only SSD doesn't need anywhere near as much overprovisioning as a traditional enterprise SSD. ZNS SSDs are still responsible for performing wear leveling, but this no longer requires a large spare area for the garbage collection process. Used properly, ZNS allows the host software to avoid almost all of the circumstances that would lead to write amplification inside the SSD. Enterprise SSDs commonly use overprovisioning ratios up to 28% (800GB usable per 1024GB of flash on typical 3 DWPD models) and ZNS SSDs can expose almost all of that capacity to the host system without compromising the ability to deliver high sustained write performance. ZNS SSDs still need some reserve capacity (for example, to cope with failures that crop up in flash memory as it wears out), but Western Digital says we can expect ZNS to allow roughly a factor of 10 reduction in overprovisioning ratios.

Better control over write amplification also means QLC NAND is a more viable option for use cases that would otherwise require TLC NAND. Enterprise storage workloads often lead to write amplification factors of 2-5x. With ZNS, the SSD itself causes virtually no write amplification and clever host software can avoid causing much write amplification, so the overall effect is a boost to drive lifespan that offsets the lower endurance of QLC compared to TLC (or beyond QLC). Even in a ZNS SSD, QLC NAND is still fundamentally slower than TLC, but that same near-elimination of background data management within the SSD means a QLC-based ZNS SSD can probably compete with TLC-based traditional SSDs on QoS metrics even if the total throughput is lower.

 

The other major hardware change enabled by ZNS is a drastic reduction in DRAM requirements. The Flash Translation Layer (FTL) in traditional block-based SSDs requires about 1GB of DRAM for every 1TB of NAND flash. This is used to store the address mapping or indirection tables that record the physical NAND flash memory address that is currently storing each Logical Block Address (LBA). The 1GB per 1TB ratio is a consequence of the FTL managing the flash with a granularity of 4kB. Right off the bat, ZNS gets rid of that requirement by letting the SSD manage whole zones that are hundreds of MB each. Tracking which physical NAND erase blocks comprise each zone now requires so little memory that it could be done with on-controller SRAM even for SSDs with tens of TB of flash. ZNS doesn't completely eliminate the need for SSDs to include DRAM, because the metadata that the drive needs to store about each zone is larger than what a traditional FTL needs to store for each LBA, and drives are likely to also use some DRAM for caching writes - more on this later.

NVMe Zoned Namespaces Explained The Software Model
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  • FunBunny2 - Friday, August 7, 2020 - link

    "Optane is byte addressable like DRAM and fairly durable, isn't it?"

    yes, and my first notion was that Optane would *replace* DRAM/HDD/SSD in a 'true' 64 bit address single level storage space. although slower than DRAM, such an architecture would write program variables as they change direct to 'storage' without all that data migration. completely forgot that current cpu use many levels of buffers between registers and durable storage. iow, there's really no byte addressed update in today's machines.

    back in the 70s and early 80s, TI (and some others, I think) built machines that had no data registers in/on the cpu, all instructions happened in main memory and all data was written directly in memory and then to disc. the morphing to load/store architectures with scads of buffering means that optimum use of an Optane store with such an architecture looks to be a waste of time until/if cpu architecture writes data based on transaction scope of applications, not buffer fill.
    Reply
  • jeremyshaw - Monday, August 10, 2020 - link

    The early 70s and 80s timeframe saw CPUs and Memory scaling roughly the same, year to year. After a while, memory advanced a whole lot slower, necessitating the multiple tiers of memory we have now, from L1 cache to HDD. Modern CPUs didn't become lots of SRAM with at attached ALU just because CPU designers love throwing their transistor budget into measly megabytes of cache. They became that way, simply because other tiers of memory and storage are just too slow. Reply
  • WorBlux - Wednesday, December 22, 2021 - link

    Modern CPU's have instruction that let you skip cache, and then there was SPARC with streaming accelerators, where you could unleash a true vector/CUDA style instruction directly against a massive chunk of memory. Reply
  • Arbie - Thursday, August 6, 2020 - link

    An excellent article; readable and interesting even to those (like me) who don't know the tech but with depth for those who do. Right on the AT target. Reply
  • Arbie - Thursday, August 6, 2020 - link

    And - I appreciated the "this is important" emphasis so I knew where to pay attention. Reply
  • ads295 - Friday, August 7, 2020 - link

    +1 all the way Reply
  • batyesz - Thursday, August 6, 2020 - link

    UltraRAM is the next big step in the computer market. Reply
  • tygrus - Thursday, August 6, 2020 - link

    The first 512-sectors I remember is going back to the days of IBM XT compatibles, 5¼ inch floppies, 20MB HDD, MSDOS, FAT12 & FAT16. That well over 30 years of baggage is heavy to carry around. They moved to 32bit based file systems and 4KB blocks/clusters or larger (eg. 64 or 128bit addresses, 2MB blocks/clusters are possible).

    It wastes space to save small files/fragments in large blocks but it also wastes resources to handle more locations (smaller blocks) with longer addresses taking up more space and processing.

    Management becomes more complex to overcome the quirks of HW & increased capacities.
    Reply
  • WaltC - Tuesday, August 11, 2020 - link

    Years ago, just for fun, I formatted a HD with 1k clusters because I wanted to see how much of a slowdown the increased overhead would create--I remember it being quite pronounced and quickly jumped back to 4k clusters. I was surprised at how much of slow down it created. That was many years ago--I can't even recall what version of Windows I was using at the time...;) Reply
  • Crazyeyeskillah - Thursday, August 6, 2020 - link

    I'll ask the dumb questions no one else has posted:
    What kind of performance numbers will this equate to?

    Cheers
    Reply

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