[svlug] More links about ssds

Marc MERLIN marc_news at merlins.org
Thu Jun 2 07:45:48 PDT 2016


On Thu, Jun 02, 2016 at 01:40:51AM -0700, Rick Moen wrote:
> TLC (triple-level cell) stores three bits per cell for greater data
> density and more capacious SSDs in the same form factor, but its
> sustained write performance is comparatively quite poor, sometimes very
> poor.
 
It's not that simple.
Samsung 850 EVO uses TLC 3D-VNAND.
It's very damn fast:
http://www.tweaktown.com/reviews/6861/samsung-850-evo-250gb-3d-nand-ssd-review/index.html
almost 100K iops, and 500MB/s read and write (limited by the Sata bus)

The way it works is by having a lot of DRAM/SLC cache, and apparently
on the 850 Evo the write performance only drops to 300MB/s when you've
filled all the caches.

> If we were all made of money, we'd ask for pure SLC NAND flash SSDs, but 
> SLC SSDs are often a really exceptional balance of functionality for the
> money.  (I would, however, try to avoid TLC flash in these devices.)
 
The best high capacity SSDs today use MLC because it's very reliable and
fast while offering twice the capacity. MLC is mature technology today.

In other words, pro drives use MLC because SLC is obsolete, and high
capacity SSDs (like my 2.5" laptop 2TB SSD) sometimes use TLC because there
is no choice, that much flash would not fit/work with MLC.
(then again, my 2TB TLC SSD now exists as an MLC drive)

More reading on the subtleties:
http://www.custompcguide.net/compare-samsung-850-pro-versus-840-evo-and-840-ssd-series/

Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/  



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