ReadyNAS RN312 重新同步速度极慢

Question

运行 2 TB RN312 OS 6.10.3 X-raid，重新同步新磁盘需要很长时间。见下文

root@nas-D5-DF-E6:~# cat /proc/mdstat
Personalities : [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
md127 : active raid1 sda3[2] sdb3[3]
      1948662656 blocks super 1.2 [2/1] [U_]
      [====>................]  recovery = 21.8% (425879424/1948662656) finish=1545559.8min speed=16K/sec

md1 : active raid1 sda2[0] sdb2[1]
      523264 blocks super 1.2 [2/2] [UU]

md0 : active raid1 sda1[2] sdb1[3]
      4192192 blocks super 1.2 [2/2] [UU]

unused devices: <none>

也尝试过设置写入缓存，但似乎无法切换到开启状态。见下文

root@nas-D5-DF-E6:~# hdparm -W 1 /dev/sda

/dev/sda:
 setting drive write-caching to 1 (on)
 write-caching =  0 (off)

有人知道如何解决这个问题吗？