I have a raid5 array on 4 NVMe drives, and the performance on the array is only marginally better than a single drive. Unlike a similar raid5 array on 4 SAS SSD or HDD, the performance on array is 3x better than a single drive, which is expected. It looks like when the single kernel thread associated with the raid device running at 100%, the array performance hit its peak. This can happen easily for fast devices like NVMe. This can reproduced by creating a raid5 with 4 ramdisks as well, and comparing performance on the array and one ramdisk. Sometimes the performance on the array is worse than a single ramdisk. The kernel version is 4.9.0-rc3 and mdadm is release 3.4, no write journal is configured. Is this a known issue? Please cc me on the email as I am not on the mail list. Thanks! -- 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
