[svlug] More links about ssds

Rick Moen rick at linuxmafia.com
Thu Jun 2 07:58:23 PDT 2016


Quoting Marc MERLIN (marc_news at merlins.org):

> 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)

It's very damn fast for modest-sided writes, but is going to slow down a
_lot_ for large ones.  300MB/s is still good, of course -- but it's also
going to have a low MTBF because of all the TLC cells.

So, it's nice that it has a 5-year warranty (according to
http://www.newegg.com/Product/Product.aspx?Item=N82E16820147372),
because there's an excellent chance you're going to be RMAing it at
least once, maybe multiple times.  Personally, I find 'long warranty' a
decent consolation prize, but all other things being equal prefer
'didn't fail'.

> 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.

That's basically what I was saying.

If we were all made of money, we'd demand that those same units be
reengineered to use all SLC at twice the cost, but because we aren't we
buy MLC-based storage and are damned happy with it as hitting the sweet
spot.




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