From mboxrd@z Thu Jan 1 00:00:00 1970 From: Victor Garcia Subject: Write mostly flag Date: Sun, 1 Jan 2017 07:37:25 +0000 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Hello all I am trying to set up a raid 1 array using an SSD and a standard SAT HDD drives. As I read, it's better to set the write-mostly flag to the HDD partition of the array to keep SSD performance times. This is the command I'm using: # mdadm --create /dev/md1 -n 2 -l 1 --metadata=0.90 --bitmap=internal /dev/nvme0n1p5 -W /dev/sda8 --write-behind I expect seeing the (W) indicator in mdstat, but this is not showing: # cat /proc/mdstat Personalities : [raid1] md1 : active raid1 sda8[1] nvme0n1p5[0] 52400064 blocks [2/2] [UU] [>....................] resync = 0.3% (175936/52400064) finish=9.8min speed=87968K/sec unused devices: But if I force later on the flag by means of the sys FS handle, then it does appear: # cat /sys/block/md1/md/dev-sda8/state in_sync # echo writemostly > /sys/block/md1/md/dev-sda8/state # cat /sys/block/md1/md/dev-sda8/state in_sync,write_mostly # cat /proc/mdstat Personalities : [raid1] md1 : active raid1 sda8[1](W) nvme0n1p5[0] 52400064 blocks [2/2] [UU] [==>..................] resync = 11.0% (5806336/52400064) finish=9.8min speed=78966K/sec bitmap: 1/1 pages [4KB], 65536KB chunk unused devices: How is it that the (W) is not showing in the first place? BTW, this is the system being used: # uname -a Linux ubuntu 4.8.0-22-generic #24-Ubuntu SMP Sat Oct 8 09:15:00 UTC 2016 x86_64 x86_64 x86_64 GNU/Linu Thanks and regards Victor