How To Check RAID Progress with /proc/mdstat

I explained how to read the /proc/mdstat in my recent post How To Identify RAID Arrays in Linux, so today is a super quick follow up using one of my systems.

I use Synology NAS in my office and disks in the storage array are getting old, so I decided to swap them out one by one in the next few months. Synology runs a Linux based proprietary OS called DSM, and ultimately it relies on software RAID configured and managed with md devices. So all the setup is done using web-based GUI, but I always like double-checking what’s going on by logging directly onto the appliance.

Here’s how I use /proc/mdstat to track the faulty disk replacement:

# cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
md2 : active raid6 sda5[9] sdb5[1] sdh5[7] sdg5[6] sdf5[8] sde5[4] sdd5[3] sdc5[2]
 17552612736 blocks super 1.2 level 6, 64k chunk, algorithm 2 [8/7] [_UUUUUUU]
 [==>..................] recovery = 13.4% (393456896/2925435456) finish=1578.6min speed=26731K/sec

This tells me:

  • md2 is the name of a RAID array device
  • RAID type is RAID6 (confirmed by raid6 personality AND level 6 words)
  • my array consists of 8 disks (sda5/sdb5/…/sdh5)
  • RAID block size is 64K
  • 7 devices are up (that’s what each of the Us mean in the [_UUUUUUU] section)
  • 1 device is down (that’s what the underscore _ means in [_UUUUUUU])
  • Array is going through a recovery procedure, we’re 13.4% there with another 26 hours (finish=1578.6min) to go
  • Speed of the RAID array recovery (effectively that’s the speed of populating the new disk with parity-based data from other disks in the array) is 26.1MB/sec (speed=26731K/sec)

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