} -----Original Message----- } From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid- } owner@xxxxxxxxxxxxxxx] On Behalf Of Info@xxxxxxxxxxxxxxx } Sent: Saturday, August 22, 2009 4:45 PM } To: linux-raid@xxxxxxxxxxxxxxx } Subject: Re: Help } } On Saturday 22 August 2009 11:12:35 Info@xxxxxxxxxxxxxxx wrote: } > Goswin says, "For scanning your videos raid10 with far layout is } probably best with } > a large read ahead." I have the RAID10 blocksize set to 1024 for the } video partition, but any idea how to set readahead? } } My gosh, it turns out this setting is astounding. You test your drive } speed with some large file, as such: } # time dd if={somelarge}.iso of=/dev/null bs=256k } } ... and check your drive's default readahead setting: } # blockdev --getra /dev/sda } 256 } } ... then test with various settings like 1024, 1536, 2048, 4096, 8192, and } maybe 16384: } # blockdev --setra 4096 /dev/sda } } Here are the results for my laptop. I can't test the HTPC with the array } yet, as it's still syncing. } 256 40.4 MB/s } 1024 123 MB/s } 1536 2.7 GB/s } 2048 2.4 GB/s } 4096 2.4 GB/s } 8192 2.4 GB/s } 16384 2.5 GB/s } } I suspect it's best to use the minimum readahead for the best speed (in my } case 1536), for two reasons: } - To save memory; } - So there isn't such a performance impact when the blocks are not } sequential. The disk cache is being used. You should reboot between each test, or use a file much bigger than the amount of RAM you have. Or use a different file each time. -- 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
