On Thu, Dec 10, 2015 at 12:54 PM, Mark Knecht <markknecht@xxxxxxxxx> wrote: > > > On Thu, Dec 10, 2015 at 10:40 AM, Dallas Clement > <dallas.a.clement@xxxxxxxxx> wrote: >> >> <SNIP> >> >> Hi John. Thanks for the help. I did what you recommended and created >> two equal size partitions on my Hitachi 4TB 7200RPM SATA disks. >> >> Device Start End Sectors Size Type >> /dev/sda1 2048 3907014656 3907012609 1.8T Linux filesystem >> /dev/sda2 3907016704 7814037134 3907020431 1.8T Linux filesystem >> > > If you're goal was to test the speed at the end of the drive it seems to me > that sda2 > should have started near the end of the drive and not presumably in the > middle? > > Probably has nothing to do with the missing 100MB/s though. > > - Mark I tried a more extreme case. Device Start End Sectors Size Type /dev/sda1 2048 6999998464 6999996417 3.3T Linux filesystem /dev/sda2 7000000512 7814037134 814036623 388.2G Linux filesystem Now I'm seeing quite a bit more difference between inner and outer. [root@localhost ~]# dd if=/dev/zero of=/dev/sda1 bs=2048k count=1000 1000+0 records in 1000+0 records out 2097152000 bytes (2.1 GB) copied, 13.4422 s, 156 MB/s [root@localhost ~]# dd if=/dev/zero of=/dev/sda2 bs=2048k count=1000 1000+0 records in 1000+0 records out 2097152000 bytes (2.1 GB) copied, 21.9703 s, 95.5 MB/s Using this this worst case inner speed my expected worst case write speed is (12 - 2) * 95.5 MB/s / 2 = 477.5 MB/s. So I guess if this really is the worst case, then the 678 MB/s sequential write speed I am seeing with RAID 6 on a large partition is not so bad. -- 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
