[svlug] More links about ssds

Marc MERLIN marc_news at merlins.org
Thu Jun 2 08:14:35 PDT 2016


On Thu, Jun 02, 2016 at 07:58:23AM -0700, Rick Moen wrote:
> 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'.

That's the theory. In practise it works better than you think
http://www.anandtech.com/show/8747/samsung-ssd-850-evo-review/4

The 1TB drive has a 2000TB endurance, which amounts to 18.7 years for a
"100GiB of Host Writes per Day with 3x Write Amplification" case.

For my 2TB drive, this would be about 40 years? (under a writing load I
don't even come close to generating on my laptop)

You need to note that Samsung's 3D VNAND is much better than normal TLC
while being about the same price.

> > 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.

You missed my point. You could not make a 2TB Sata SSD for my laptop made
out of SLC today. It just would not fi, and it would be 3x the cost of TLC :)

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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