On 15/02/13 09:42, Chris Murphy wrote: > (digging back through some things now that the higher priority tasks > appear covered) > > > On Feb 8, 2013, at 2:42 PM, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> > wrote: > >> These tests use 4KB *aligned* IOs. > > It seems SSD's commonly now are 8KB paged. [1] [2] At least on OS X > with a Samsung 830 SSD, I'm finding a meaningful difference between > alignment on 4K vs a 1M alignment. [3] > > Sequential write and rewrite aren't affected. Sequential Input is > affected, 5.6% improvement by 8K aligning. Random Seeks see an 87% > improvement with 1M alignment. I haven't retested to see if an 8K > alignment produces as good a result as a 1M alignment. I haven't > tested the full effect of Bonnie++ chunk size which is 8KB by > default; but in all tests so far there's no meaningful difference > between a chunk size of 4KB and 8KB. > > It's kind of annoying that SSD manufacturers aren't reporting a > "physical sector" mapped to the SSD page size; similar to how 512e AF > HDDs report 512 byte logical, 4096 byte physical sectors. The > implication of an SSD reporting a 512 byte physical sector is that > alignment doesn't matter. I think it might matter. So assuming I don't mind wasting a few MB per disk (I was leaving empty space at the end of the partition anyway), what would I need to instruct fdisk and/or md to do to get the alignment right? Current partition/disk is as follows: fdisk -l /dev/sdc Disk /dev/sdc: 480 GB, 480101368320 bytes 255 heads, 63 sectors/track, 58369 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sdc1 1 58000 465884968 fd Lnx RAID auto fdisk -ul /dev/sdc: Disk /dev/sdc: 480 GB, 480101368320 bytes 255 heads, 63 sectors/track, 58369 cylinders, total 937697985 sectors Units = sectors of 1 * 512 = 512 bytes Device Boot Start End Blocks Id System /dev/sdc1 63 931769999 465884968 fd Lnx RAID auto Thanks, Adam -- Adam Goryachev Website Managers www.websitemanagers.com.au -- 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
