History
LMR vs CMR vs SMR
Hard drives store data in “tracks,” which are circular paths typically oriented in concentric rings on the top and bottom surfaces of a hard disk platter. Each hard disk unit can contain multiple platters, which allows the drive to store more data.
Historically, manufacturers have increased storage capacity in hard disk models by either increasing the number of platters in the drive or increasing the write density on the disk. In the past, the circular tracks written to the disk never overlapped. The data storage industry calls this “Perpendicular Magnetic Recording” (PMR) or “Conventional Magnetic Recording” (CMR).
Recently, a new technique for increasing write density called “Shingled Magnetic Recording” (or SMR) has emerged. SMR drives write data using a special method that partially overwrites previously written tracks on a hard disk platter. The manufacturers use the analogy of roof shingles that partially overlap each other to explain this technique, which is where the “shingled” part of the name comes from.
While SMR drives increase capacity for lower cost (because the drives can use fewer platters than a CMR drive at the same capacity), the way they work also comes with a speed penalty. When you copy data to an SMR drive, the drive temporarily stores the data in a special cache area and uses idle time later to organize it into shingled regions on the platter. Long, sustained writes suffer speed penalties because if the cache fills up, each time an SMR drive overwrites part of a previous track, it must read and re-write the “partially covered” underlying data as well. So SMR drives can perform dramatically slower than CMR drives.
SMR’s slow performance led to a controversy in 2020 and 2021 when people realized that manufacturers were selling SMR drives without labeling them (in both external hard disks and internal drives), arguably selling an inferior product without warning customers. Some of these complaints even led to a $2.7 million class-action settlement with Western Digital in 2021.
– howtogeek
M.2 = Form Factor
HAMR
Multi-actuator drives:
https://www.seagate.com/products/enterprise-drives/exos-x/2×18/
high resistivity: no change=0
ECC: ensure no data is lost
Classical magnetic recording (CMR)
Step 2: write both top and lower track with new data
Step 3: write top track with old data from DRAM
needs buffering & causes extra read/write steps
small focused laser to heat region that is actively being written to
by heating domain, the magnetic region can be more easily influenced or coerced to orient in particular direction
so we can continue to shrink the size of magnetic domain Don’t know why 🙁
References:
- Chen, Ben M. Lee, Tong H. Hard Disk Drive Servo Systems 2nd Edition. Springer, 2006.
- Jacob, Bruce. Ng, Spencer W. Wang, David T. Memory Systems, Cache DRAM, Disk. Morgan Kaufmann, 2008.
- Magnetic Hard Disk https://www.sciencedirect.com/topics/…
- Modern HDD Technologies that are bringing hard disks back. Sullivan, Erin. https://www.techtarget.com/searchstor…
- Magnetic Recording on Nanostructures https://www.tu-chemnitz.de/physik/OFG…
- Hard Disks Give New Technologies A Spin. Feldman, Michael. https://www.nextplatform.com/2019/10/…
- Hard Drives 101: Magnetic Storage. Bestofmedia Team. https://www.tomshardware.com/reviews/…
- Lasers vs. Microwaves: The Billion Dollar Bet on The Future of Magnetic Storage. Nordrum, Amy. https://spectrum.ieee.org/lasers-vs-m…
- Wikipedia contributors. “Hard Disk Drives”. “Magnetic Storage”. “Perpendicular Magnetic Recording”. “Shingled Magnetic Recording”. “Storage Density”. Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, Visited December 2022
Asianometry: The Birth, Boom and Bust of the Hard Disk Drive
Piezo-actuators at tip:
https://link.springer.com/article/10.1007/s00542-023-05460-7
https://link.springer.com/content/pdf/10.1007/s00542-023-05460-7.pdf
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