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 -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
