Re: Hardware vs Software RAID

On Wed, 25 Jun 2008, Merlin Moncure wrote:
>> Has anyone done some benchmarks between hardware RAID vs Linux MD software
>> RAID?
>
> I have here:
> http://merlinmoncure.blogspot.com/2007/08/following-are-results-of-our-testing-of.html
>
> The upshot is I don't really see a difference in performance.

The main difference is that you can get hardware RAID with
battery-backed-up cache, which means small writes will be much quicker
than software RAID. Postgres does a lot of small writes under some use
cases.

Without a BBU cache, it is sensible to put the transaction logs on a
separate disc system to the main database, to make the transaction log
writes fast (due to no seeking on those discs). However, with a BBU cache,
that advantage is irrelevant, as the cache will absorb the writes.

However, not all hardware RAID will have such a battery-backed-up cache,
and those that do tend to have a hefty price tag.

Matthew

--
$ rm core
Segmentation Fault (core dumped)