On Fri, Aug 22, 2008 at 06:15:23PM -0500, Michael S. Zick wrote: > 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. that matches my experience with some 3ware cards where actually JBOD and software raid is the superior solution, but if you are looking at pure read/write throughput, my old card reached 160M/s on two channels easily (sustained transfer) which is mostly limited by the raid layout and the 80-100M/s sustained transfer rate of the disks but what's more important, is that the seek time is a lot better than on a single disk ... > 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. the card in question is 8x, the slot 16x, so I think that should be fine > 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). one 16x is actually enough, I don't need (and do not have) a graphics card in that machine (works headless over serial port and GB network) > If Herbert wants fast compiles, he should keep his kernel tree in a > RAM disk on a 32 or 64Gbyte ram machine. trust me, I investigated this path, but as it is perfect for compiling one and the same kernel (2-4GB are usually enough for that), this doesn't work that well for hard linked kernel trees which in total cover more than a terrabyte of space (plus tons of temporary clones) for repeated builds, the kernel does a good job with caching, so that happens basically out of RAM, and so does the repeated diff between versions > 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 anyway, I'm going to replace that card in the near future, so if somebody wants to help there, let me know, if not, so be it :) TIA, Herbert > > Ed W