5 ms·
The highest capacity drives are not SMR, they're CMR. Why? Because nobody who stores large amounts of data wants to buy SMR drives. SMR drives are garbage an
by bcrl 7y ago
The highest capacity drives are not SMR, they're CMR. Why? Because nobody who stores large amounts of data wants to buy SMR drives. SMR drives are garbage and will continue to remain garbage. They're a dead end technology.
For those wondering why SMR drives are so bad, consider the following: SMR drives basically make the same trade-off that flash makes, but with a magnetic media that has a significant seek time and bandwidth penalty compared to flash. Any time a non-sequential write is made to an SMR drive, the whole "block" (which can be many megabytes in size) needs to be read from the disk into memory, written out somewhere else on the disk after which you can finally perform the equivalent of a flash sector erase and start writing data out sequentially again. The catch is that your hard drive can only perform sequential i/o at maybe 200MB/s vs the 3GB/s flash can. Flash sectors are also measured in kilobytes (128KB is a common size), while SMR "sectors" can end up being 16-128MB in size. Do the math. The latency is a disaster as we're talking hundreds to thousands of milliseconds of latency to do an erase. Flash can erase a sector in a millisecond, and you can have multiple erases occurring in parallel across multiple planes and dies. An SMR drive can have exactly 1 erase operation in flight at a time.
If SMR drives were of any value, you'd see them at the high end of the capacity spectrum. It's funny how those products don't seem to exist.
- Wowfunhappy 7y agoBut we do use SMR drives at the high end of the capacity spectrum! Dropbox uses them heavily in their data centers[1], estimating that 40% of their data would be stored on SMR drives at the end of 2019. Now, that's a data center, but don't consumers sometimes have similar cold-storage use cases? As long as they know what they're buying? [1] https://dropbox.tech/infrastructure/smr-what-we-learned-in-our-first-year https://dropbox.tech/infrastructure/smr-what-we-learned-in-o...
- bcrl 7y agoThe reads like a fluff piece that just doesn't add up. Dropbox mentions testing 14TB SMR drives in the post from June 12 2018 https://www.anandtech.com/show/15457/western-digital-roadmap-updates-energy-assisted-recording-multistage-actuators-zoned-storage https://www.anandtech.com/show/15457/western-digital-roadmap... . If I have a look on Amazon right now, the largest HDDs are 16TB CMR drives, not SMR. Anandtech has a post based off of WD's press release from December 23rd 2019 here https://www.anandtech.com/show/15457/western-digital-roadmap-updates-energy-assisted-recording-multistage-actuators-zoned-storage https://www.anandtech.com/show/15457/western-digital-roadmap... . The energy assisted MAMR drive is 18TB in capacity, while the SMR drive is 20TB in capacity. Where's the 25% capacity benefit? Shouldn't the SMR drive offer a capacity of 22.5TB? Have a look at this https://www.anandtech.com/show/15457/western-digital-roadmap-updates-energy-assisted-recording-multistage-actuators-zoned-storage https://www.anandtech.com/show/15457/western-digital-roadmap... article at Anandtech posted January 31st 2020. Note the side by side comparisons of projected growth of SMR drive capacity shipments. SMR growth projections are always right around the corner in the next 1-2 years. Why is this? Quite simply the market doesn't want SMR. Non-SMR technology continues to improve, eliminating SMR's capacity advantage after a period of time without SMR's orders of magnitude performance penalties. If SMR was more than just a one time 25% capacity advantage it might be worth buying into. But it doesn't. It's a technology in search of a market that just doesn't exist because of all the downsides. HAMR and MAMR are the promising technologies to increase HDD capacity, not SMR.