[OpenIndiana-discuss] Recommendations for fast storage

[Andrew Gabriel]

Mehmet Erol Sanliturk wrote:
> I am not an expert of this subject , but with respect to my readings in
> some e-mails in different mailing lists and from some relevant pages in
> Wikipedia about SSD drives , the following points are mentioned about SSD
> disadvantages ( even for "Enterprise" labeled drives ) :
> 
> 
> 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 .

That's why some of them include their own momentary power store, or in
some systems, the system has a momentary power store to keep them powered
for a period after the last write operation.

> 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 )  .
> 
> SLC ( Single-Level Cell ) SSD units have much more long life span , but
> they are expensive with respect to MLC SSD units .
> 
> SSD units may fail due to write wearing in an unexpected time , making them
> very unreliable for mission critical works .

All the Enterprise grade SSDs I've used can tell you how far through their
life they are (in terms of write wearing). Some of the monitoring tools pick
this up and warn you when you're down to some threshold, such as 20% left.

Secondly, when they wear out, they fail to write (effectively become write
protected). So you find out before they confirm committing your data, and
you can still read all the data back.

This is generally the complete opposite of the failure modes of hard drives,
although like any device, the SSD might fail for other reasons.

I have not played with consumer grade drives.
 
> Due to the above points ( they may be wrong perhaps ) personally I would
> select revolving plate SAS disks and up to now I did not buy any SSD for
> these reasons .
> 
> The above points are a possible disadvantages set for consideration .

The extra cost of using loads of short stroked 15k drives to get anywhere
near SSD performance is generally prohibitive.