On Fri August 22 2008 17:52, Ed W wrote: > Michael S. Zick wrote: > > > > The true advantage of a hardware card, is you only read/write > > the storage data once over the PCIe link. > > > > > I agree in theory, but I have been desperately disappointed with a two > 3Ware cards of various generations. They struggled to get read or write > performance to match a half that of a single drive in a 4 drive raid5 > config. > It is very easy to build a card in a 16x form factor, perhaps using only a single (1x) channel; These cards would be Bragging Rights and/or Marketing Rights only cards. Ah, but building a 16x form factor card with electronics that can run that fast - - much harder, also much too expensive. > Some of the limitations looked very much like those of the PCI > bus and indeed 3wares benchmarks suggested that you needed faster than > PCI to get >20-40MB/sec out of their cards (ugg). > The PCI bus is too slow, even the double width, double speed version. Even a 2x card can run into bandwidth limitations. Keep in mind, PCI is a half-duplex, shared, bus. The 16x and 32x PCIe is driven directly by the bridge chipset, no PCI bus involved getting to/from RAM. At least, not if your pocket book is deep enough. This is another reason why it is hard to find a motherboard with more than one 16x or 32x slot (in transfer width, not just connector size). If Herbert wants fast compiles, he should keep his kernel tree in a RAM disk on a 32 or 64Gbyte ram machine. That would probably cut him down to a single serving of his favorite beverage per compile. Mike > To me this looked > very much like the data was being transferred too many times versus > theory (also I discovered later that nearly all these hardware cards > can't do xor fast enough to keep up with a sensible modern disk, hence > software raid5 can often be faster because you aren't lagging on the xor > engine...) > > I think the safe benchmark is all in software and be very cautious of > these hardware SATA cards. That said, the various scsi cards I have > tried absolutely scream. Why there are only cr*p sata hardware cards I > just don't understand? > > Oh well > > Ed W > >