On Mon, Dec 14, 2009 at 1:06 AM, Matthieu Patou <mat@xxxxxxxxx> wrote: > Hello Goswin, >> Software raid1 will write twice as much data. That means twice as much >> data goes over the system bus and into the controler cache. >> Effectively you have halve the cache size. Maybe that is all you see. >> >> MfG >> Goswin >> > Your idea seems logical, and I took a few hours today to verify it and it's > the case as accessing the disk without software raid leads to almost the > same result as with hardware raid. > > Matthieu. > -- > 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 > Thinking about it, the doubling of data going over the system bus part is correct. You must still push the operation out to each device's buffer. However for -most- modern systems the system-bus will not be the bottleneck for a reasonable number of drives. Further the later half which I'd skimmed over the first time is utterly incorrect. Each drive would still only see the commands targeting that drive. That should be virtually the same if not identical to the single-drive case. The two most likely bottlenecks are single-drive write speed, and any IO barriers that are used to ensure file system consistency in the event of sudden interruption. -- 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
