On Wed, 2007-07-18 at 12:26 -0400, Justin Piszcz wrote: > I will try these options during future testing and re-visit the speeds of > regular HW RAID5, thanks! I know they are part of the 3ware doc and I > need to re-bench with these. 3Ware cards should be "tuned" for optimal performance, especially if you have the battery backup unit (BBU) on the 9500 and later cards** , and some of the settings can be made more "lax." It's hard to gage hardware RAID v. software RAID, especially since the latter can cache commits -- at least from the standpoint of various benchmark utilities (like Bonnie). There are various arguments that go back'n forth on this. But if you're using 3Ware in JBOD with software RAID because you've been fed the standard and quite _incorrect_ statement that you can do hot-swap, understand that you can't get fully supported hot-swap without using the 3Ware's hardware RAID volume management (with the segmentation of its on-board microcontroller intelligence). 3Ware gets a bad rep because too many MD advocates out there proliferate the 3Ware supports hot-swap in JBOD -- you need to leverage kernel hot-plug and other kernel facilities for hot-swap if you use MD software RAID. You don't need to use the various kernel facilities if you let the 3Ware intelligence management the volumes. That's a major, major, missing piece of information that I've seen far too many MD advocates omit. -- Bryan **NOTE: Earlier cards (6000-9000, pre-9500) only use SRAM logic, no DRAM cell, so they don't need a BBU. Long story, SRAM combinational circuits don't need to be "refreshed" and the board's capacitors can store enough charge to keep values in SRAM circuits (at least long enough to flush to disk or once the disks are powered again). Of course, on those earlier cards, the SRAM is small, too small to buffer most sustained RAID-5 writes so I'd only use RAID-10 on them. -- 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
