Everything I Know About SSDs

Post by 0xff00ffee » Wed, Jan 15, 2020, 10:29 PM UTC

wtallis wrote: post #96

0xff00ffee wrote: post #90

Excellent summary. One thing he left off: some SSDs continue to copy/erase blocks even if there is nothing new to write because multi-level cell state does degrade over time. There is a concern that some MLC drives will suffer bit corruption over time if not regularly power up to allow this in the background. Citation needed: I only recall this when I was interviewing to work for Western Digital many years ago.

This problem was most prominent right before the switch to 3D NAND, when planar NAND dimensions were at their smallest and the consumer market had already mostly switched over to 3 bit per cell TLC rather than 2bpc MLC. In the worst case, we were down to about 8 electrons difference between cell voltage states. That's now been relaxed by 3D NAND allowing for larger cell sizes, and most 3D NAND also switched from floa…

Post by nitrogen » Wed, Jan 15, 2020, 10:32 PM UTC

toast0 wrote: post #111

ascar wrote: post #75

Earlier quoted context omitted.

I'm really interested in how you benchmarked that? Is there a "simple" way to specify the physical location on a HD data should be written to?

To build on the sibling comment, the simple way to benchmark this is with an empty hard drive, make a series of partitions in order: 1) start of drive partition 2) spacer 3) middle of drive partition 4) spacer 5) end of drive partition Make 1,3, and 5 the same size, and then run raw disk benchmarks against them. The usual pattern is, like a record, the data begins at the edge of the platter and you'll get higher tran…

Post by mehrdadn » Wed, Jan 15, 2020, 10:48 PM UTC

wtallis wrote: post #78

ascar wrote: post #75

Earlier quoted context omitted.

I'm really interested in how you benchmarked that? Is there a "simple" way to specify the physical location on a HD data should be written to?

Hard drives generally use a fairly simple linear mapping between LBAs and physical location. Low LBAs are on the outer edge of the platter where transfer speeds are highest, and high LBAs are on the inner edge where speeds are lowest. Unlike SSDs, hard drives don't need wear leveling, so there's no reason to break from that pattern except in the relatively rare instance of damaged sectors. At smaller scales, the layo…

Post by chadcmulligan » Wed, Jan 15, 2020, 10:49 PM UTC

FpUser wrote: post #113

pkaye wrote: post #66

Earlier quoted context omitted.

I used to work on SSD firmware for a long time. There is a lot of technology and individuals involved but to be honest I find learning on the present day web development stack more daunting at times!

That is because the firmware is all about efficiency and reliability is strictly business no f..ng around. This is at least from my experience. Web is like: look ma, new shiny stack, gotta use it. The amount of tooling involved in creation of even simple things is often staggering without any real need for it. And often if you do not approach webdev in "politically correct" way you can be laughed out of the door.

Post by AdamJacobMuller » Wed, Jan 15, 2020, 10:54 PM UTC

geek_at wrote: post #138

Stratoscope wrote: post #128

"Website is sleeping" 000webhost lives up to its name! In the meantime: https://archive.is/20200115095916/http://kcall.co.uk/ssd/ind...

strange. archive.is is resolving to 127.0.0.5 for me even if I do nslookup archive.is 1.1.1.1 Server: one.one.one.one Address: 1.1.1.1 Name: archive.is Address: 127.0.0.5