On Wed, 2007-07-18 at 13:17 +0200, Giuseppe Ghibò wrote: > Indeed not exists for PCI-e but Oden has spotted this PCI-X card > (which is around 97$), based on marvell chipset: > http://www.supermicro.com/products/accessories/addon/AoC-SAT2-MV8.cfm Yes! There are several Broadcom and Marvell ASICs that are eight (8) SATA (and now even some SAS) channels in a single chip, of which, there are several vendors selling them for $100 boards. You do _not_ want an on-board intelligence being an "intermediary" with software RAID, you want _direct_ access to the SATA (or SAS) channels. Besides, they are cheaper. Justin Piszcz ha scritto: > I am sure one of your questions is, well, why use SW RAID5 on the > controller? Because SW RAID5 is usually much faster than HW RAID5, > at least in my tests ... Benchmarking direct disk access is a rather poor test of hardware RAID. to truly evaluate if the off-load from the main system interconnect** that a hardware RAID gives you, you need to benchmark your actual _server_ application -- one with MD, the other with hardware RAID. That's where you can tell if hardware RAID is going to buy you anything. **NOTE: It's the system interconnect bottleneck that is of concern, not so much the CPU. A modern, superscalar, multi-core x86-64 CPU can do XORs in its sleep, with just MMX (won't even peg your CPU 10%). It's the LOAD/STO push just to get the XOR that ties up your system interconnect (often with your CPU only being 10% busy if your application is not processor-bound, but I/O ;-) that's the problem. It's been my experience that for web services, hardware RAID buys you _little_, because you're more processor bound than I/O bound, so you have cycles you can use while your interconnect is doing I/O processing. But more on the database and file server side, I pair a hardware RAID (e.g., AMCC/3Ware PPC400-based or Areca IOP/X-Scale-based) with a RX TOE (_Receive_ TCP Off-load Engine) HBA "NIC" (e.g., LeWiz 4-port GbE PCIe), which keeps the system inteconnect free for pushing the application data (instead of doing what is, essentially, "programmed I/O" for the XOR software RAID operation). Again benchmark your server _application_, not the disk I/O. -- Bryan J. Smith Professional, Technical Annoyance mailto:b.j.smith@xxxxxxxx http://thebs413.blogspot.com -------------------------------------------------------- Fission Power: An Inconvenient Solution - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
