I'm retired, haven't worked in the industry since 2000 - disabled veteran with serious back and knee problems.
OK, so much for the basic issue of qualifications - - - yet I remain an active home/hobbiest engineer in the computer, electronic, and bio-med fields, with continuous contact with leading engineers in half dozen companies.
The following BOTE off-the-top of my head calculations have been examined, and accepted, by these engineers, and the issue has been incorporated as product-purchase holds on ALL WD devices for the duration.
- - -
1) ASSUME an 8 layer shingle - which I believe is the standard
2) randomized data position for updates will be 1/2, or 4 layers
3) data has to be READ and buffered before WRITING - 4 revolutions of the platter to READ
ASSUMING a single-track step is within the time interval of a single spin - 8.33 mSec @ 7200 RPM
7200 RPM is the sweet spot for speed & longevity - anyway, not too relevant to the time PENALTY
4) Then you need a revolution to reset the heads for WRITE - MAYBE TWO TWIRLS if it's a full 8-track
5) 4 more spins for the WRITE set
6) TOTAL = 9 or 10 spins, call it 9.5? - 8-track change may need 10+ mSec
7) 17 hours for a Conventional format rebuild - X - 9.5 (spin ratio factor) == 6 days, 17.5 hours for SMR
8) NOW add-in the diddle factor added for some use during rebuild, and it's 8 to 9+ days ! ! !
THIS IS EQUAL TO THE OBSERVED REBUILD TIME IN THE ARTICLE === 9+ days, AND it describes the processing that causes the excess time for Shingle format rebuilds.
ALSO, remember that this assumes only a few contiguous sectors. IF there are too many, then you will get ANOTHER spin tacked onto the rebuild time factor.
BTW - here's a short list of the SMR WD drives if you didn't get to it
3.5 WD Red 2TB, 3TB, 4TB, 6TB (SKUs: WD20EFAX, WD30EFAX, WD40EFAX, WD60EFAX)
3.5 WD Blue 2TB, 6TB (SKUs: WD20EZAZ, WD60EZAZ)
2.5 WD Blue 1TB, 2TB (SKUs: WD10SPZX, WD20SPZX)
2.5 WD Black 1TB (SKU: WD10SPSX)
cheers, y'all . . .