> [ ... ] compares the Linux Kernel RAID code to an $800 > hardware RAID card and might be of interest to list members: > http://www.linux.com/feature/140734 Perhaps they could, if they were accompanied by vital details like the exact experimental conditions used, because those who talk of Bonnie++ and Iozone etc. as if they were mostly useful benchmarks tend, in my experience, to forget about the several pitfalls one can get into. I have seen several speed tests in this mailing lists from the usual suspects, and most range from the grossly meaningless to the rather misleading. The comparison above is somewhat pointless to read without knowing which elevator, readhead, plugging/unplugging, kernel version (even if some ot these are somewhat implicit in Fedora 9, e.g. CFQ) and so on; also whether caching was enabled or not between runs (even if the use, if properly done, of 100G datasets with 2G memory might reduce the influence of that, except of course for the CPU cost). The "using equal-sized partitions" bit is also worrying: it is not clear whether the sw RAID is built on the partitions or viceversa. This has a huge influence on alignment, and I am not sure that "chunk and stride aligned to the RAID where possible" can be relied upon without seeing exactly how the filesystems were created. Also, the graphs seem mislabeled, as all results are reported as coming from Bonnie++, including the metadata ones which are more likely to be coming from Iozone. Also for comparison they should have been drawn to the same Y scale. There are so many nonlinearities in the Linux IO subsystem where one can get wildly different results with small changes in obscure parameters (or large changes in parameters that should matter little, like the block device readahead) that overall tests like the above are not that useful without a list of the exact conditions. Overall however most of the results are within the boundaries of very rough plausibility, but the devil is in the details. The overall conclusions that alignment matters a great deal with parity RAID and that a system with a recent CPU and a PCIe bus can outperform in most cases a hardware RAID card are not that novel... -- 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
