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Hi Fabrizio, assume a small rack of 20 1U/2U dual-quad-cores + 8 disks each. Such a rack can process: 20 * 8 * 15 = 2.4GB/s (15MB/s ROOT compressed file reading speed, I/O bound query). Now such a rack would need a switch with a dual 10GB uplink to get just 2 GB/s in over the network. Now add another couple of such racks. You would need a disk pool + a lot of 10GB eth equipment per rack. You still think it scales better than having disks close to the CPU's? Cheers, Fons. Fabrizio Furano wrote: > Hi Pablo, > > that's very interesting, and I agree completely with your conclusion, > i.e. in most cases the lan data access is more efficient and scales > better with respect to local disk access. Many times this is not very > well understood by people, always striving to keep local files at any cost. > > It would be very interesting to have a comparison between the > performance in proof between a dcache storage and an analogous xrootd > storage, which is the default solution for that. With the same pool of > workers of course. > > From what I've understood, dcache uses a read ahead mechanism (at the > client side), while xrootd uses a scheme which is mixed with informed > async prefetching. > > Fabrizio > > Pablo Fernandez ha scritto: >> Hi all, >> >> I would like to share with you some information about my testings of >> performance in Proof with different storage schemas. >> http://root.cern.ch/phpBB2/viewtopic.php?t=6236 >> >> I have translated this topic to the Proof Forum since seems to me more >> Proof-related than just xrootd, I hope you don't mind. >> >> BR/Pablo > -- Org: CERN, European Laboratory for Particle Physics. Mail: 1211 Geneve 23, Switzerland E-Mail: [log in to unmask] Phone: +41 22 7679248 WWW: http://fons.rademakers.org Fax: +41 22 7669640