Re: ram/raid1

[Francesco Pietra <frapietra@alice.it>]

Hi Erik:
thank you from both the scientific and the commercial point of view
Francesco Pietra

On Friday 07 April 2006 11:18, Erik Mouw wrote:
> On Fri, Apr 07, 2006 at 06:59:29AM +0200, Francesco Pietra wrote:
> > n setting up a workstation with
> >
> > --two amd6a 265 opterons dual core
> > --Tyan K8WE S2895SA3NRF main board
> > --two 360GB raid1 hd (raid 1 software by debian)
> > --ram 2GB (Kingston KVR400D4R3A/2G - DDR 400 Ecc Registered), is any
> > reason to prefer two slots of memories 1GB each instead of a single 2GB
> > slot?
>
> Most certainly.
>
> > The technician here maintains that two slots are needed to have needed
> > two channels for raid1; it is unclear to me.
>
> The memory slots have nothing to do with the RAID. The reason you want
> 2x 1GB is that dual (or more) Opteron designs are not SMP (Symmetric
> Multi Processor), but NUMA (Non-Uniform Memory Architecture). With SMP
> the two CPUs share the same bus to memory, but with NUMA each CPU has
> some local memory connected to a local memory bus. The other CPU can
> still get to that memory, but it's a bit slower. If you would only put
> in 1x 2GB, you will severely slow down the other CPU cause it has to go
> through the other CPU to do memory accesses.
>
> To see what I mean, get the board datasheet at
> ftp://ftp.tyan.com/datasheets/d_s2895_101.pdf and look at the block
> diagram on the second page. The Linux virtual memory subsystem is NUMA
> aware, especially in the latest kernels (i.e.: 2.6.15 and better): it
> will take care managing the memory in such a way to minimize the
> amount of traffic between the CPUs.
>
> > Incidentally, the 2GB Kingston is charged in Italy six hundred euros,
> > that is more than twice the price in US. This is to recognize that we can
> > circumvent the market leader software houses (and be more efficient) but
> > we cannot avoid the system in our country which favors handlers against
> > citizen (and against scientific research activities). The results of such
> > policy are under the eyes.
>
> You can order memory everywhere in the EU, that's what the "no
> obstacles for trading goods" rules are for. If you can find memory
> cheaper in (for example) Germany, buy it over there and have it shipped
> to Italy. Be sure to let your Italian vendor know that he missed a
> sale.
>
>
> Erik