Re: RAID and SSD configuration question

On Tue, Oct 20, 2015 at 3:14 AM, Birta Levente <blevi(dot)linux(at)gmail(dot)com> wrote:
> Hi
>
> I have a supermicro SYS-1028R-MCTR, LSI3108 integrated with SuperCap module
> (BTR-TFM8G-LSICVM02)
> - 2x300GB 10k spin drive, as raid 1 (OS)
> - 2x300GB 15k spin drive, as raid 1 (for xlog)
> - 2x200GB Intel DC S3710 SSD (for DB), as raid 1
>
> So how is better for the SSDs: mdraid or controller's raid?

I personally always prefer mdraid if given a choice, especially when
you have a dedicated boot drive. It's better in DR scenarios and for
hardware migrations. Personally I find dedicated RAID controllers to
be baroque. Flash SSDs (at least the good ones) are basically big
RAID 0s with their own dedicated cache, supercap, and controller
optimized to the underlying storage peculiarities.

> What's the difference between Write Back and Always Write Back with supercap
> module?

No clue. With spinning drives simple performance tests would make the
caching behavior obvious but with SSD that's not always the case. I'm
guessing(!) 'Always Write Back' allows the controller to buffer writes
beyond what the devices do.

merlin