Keld Jørn Simonsen wrote: > Hmm, > > Why is the command > > blockdev --setra 65536 /dev/md0 > > really needed? I think the kernel should set a reasonable default here. The in-kernel default for a block device is 256 (128k) which is way too low. the MD subsystems tries to be a bit smarter and assigns the md device readahead according to the number of devices/raid level. For streaming (i.e. file sever) these values are also too low. LVs can take a readahead specification at creation time and use that, but this is manual. It is arguable what the typical workload is, but I would lean towards big long linear reads (fileserver) vs short scattered ones (database). The real solution to the problem was proposed a long time ago, and it seems it got lost in the attic: http://lwn.net/Articles/155510/ -- 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
