Am 2013-09-03 00:16, schrieb Chris Tapp:

On 2 Sep 2013, at 22:45, Christian Gagneraud wrote:

On 03/09/13 00:35, Burton, Ross wrote:
Hi Ross,

On 2 September 2013 06:05, Christian Gagneraud <chgans@...> wrote:

So right now, I'm thinking about:
- CPU: Xeon E5, maybe 2 x E5-2670/90, for a total of 16 cores (32 threads)
- Hard drives: 500GB, 1 TB or 2 TB (ideally with RAID if it can speed up the
builds)

RAID-5 seems to be what i am after.

Isn't RAID-5 going to be slower, especially if it's software? RAID 1
is probably better as you'll potentially double the write speed to
disk. I use a couple of Vertex SSDs in RAID 1 giving a theoretical
write speed near to 1GBs. Write endurance is possibly a concern, but
I've not had any issues using them on a local build machine. I would
probably look at some higher end models if I was going to run a lot of
builds. A lot less noise than hard drives ;-)

Hi, this sounds interesting to me.

Having a brief look into wikipedia ( http://en.wikipedia.org/wiki/RAID ) tells me that RAID-1 gives no increase in write speed at all (for sequentioal operations), by theory: 1x ...while a RAID-5 at least in theory, should give you: (n-1)x, assumed the hardware is fast enough to support it (RAID controller!).

Having had a small conversation here, I was told we even made experiences on having HW RAID being slowed down by the RAID controller, and its limitation of I/O-operations, that still could be handled. So, it seems to me one motivation why using SW RAID instead of HW RAID is exactly to overcome this limitations of having the bottleneck of a RAID controllers.

Question, running RAID-5, have you tried to adjust the chunck size? In our case most I/O operations are on relatively small text files and may require some adjustment to the RAID chunck size value in respect to that fact.

BR,
Lothar Rubusch