Re: Scaling with memory & disk planning

> If you are looking for the best performance, why go with a RAID5 as
> opposed to a RAID1+0 (mirrored stripes) solution?  Understandably RAID5
> is a cheaper solution requiring fewer drives for redundancy but, from my
> experience, RAID5 chokes horribly under heavy disk writing.  RAID5
> always requires at least two write operations for every block written;
> one to the data and one to the redundancy algorithm.
>
> Is this wrong?

  Here's my take on it...

  If you have enough RAM to keep everything buffered/cached, and fsync()
is turned off, then the speed of the disk subsystem becomes vastly less
important - you'll only read the data once (first couple of queries), and
then the disks will sit idle.  The lights on the disks on my DB machine
only flicker once per minute or less.   If that's the case, then I'd
rather use RAID 5 with a hot-spare or two, to increase storage capacity
over 1+0, and speed at reading as well.

  Of course, if you write tremendous amounts of data, and your data set is
larger than you can cache/buffer, that all flies out the window.

steve