[OpenIndiana-discuss] Recommendations for fast storage

[Edward Ned Harvey (openindiana)]

> From: Mehmet Erol Sanliturk [mailto:m.e.sanliturk at gmail.com]
> 
> SSD units are very vulnerable to power cuts during work up to complete
> failure which they can not be used any more to complete loss of data .

If there are any junky drives out there that fail so dramatically, those are junky and the exception.  Just imagine how foolish the engineers would have to be, "Power loss?  I didn't think of that...  Complete drive failure in power loss is acceptable behavior."   Definitely an inaccurate generalization about SSD's.  There is nothing inherent about flash memory as compared to magnetic material, that would cause such a thing.

I repeat:  I'm not saying there's no such thing as a SSD that has such a problem.  I'm saying if there is, it's junk.  And you can safely assume any good drive doesn't have that problem.


> MLC ( Multi-Level Cell ) SSD units have a short life time if they are
> continuously written ( they are more suitable to write once ( in a limited
> number of writes sense ) - read many )  .

It's a fact that NAND has a finite number of write cycles, and it gets slower to write, the more times it's been re-written.  It is also a fact that when SSD's were first introduced to the commodity market about 11 years ago, that they failed quickly due to OSes (windows) continually writing the same sectors over and over.  But manufacturers have been long since aware of this problem, and solved it by overprovisioning and wear-leveling.

Similar to ZFS copy-on-write, which has the ability to logically address some blocks and secretly re-map them to different sectors behind the scenes...  SSD's with wear-leveling secretly remap sectors during writes.


> SSD units may fail due to write wearing in an unexpected time , making them
> very unreliable for mission critical works .

Every page has a write counter, which is used to predict failure.  A very predictable, and very much *not* unexpected time.