5.9.9. Day to Day Management of RAID Arrays

There is little that needs to be done to keep a RAID array operating. As long as no hardware problems crop up, the array should function just as if it were a single physical disk drive. However, just as a system administrator should periodically check the status of all disk drives on the system, the RAID arrays' status should be checked as well.

5.9.9.1. Checking Array Status With /proc/mdstat

The file /proc/mdstat is the easiest way to check on the status of all RAID arrays on a particular system. Here is a sample mdstat (view with the command cat /proc/mdstat): 
 Personalities : [raid1] read_ahead 1024 sectors md1 : active raid1 hda3[0] hdc3[1] 522048 blocks [2/2] [UU] md0 : active raid1 hda2[0] hdc2[1] 4192896 blocks [2/2] [UU] md2 : active raid1 hda1[0] hdc1[1] 128384 blocks [2/2] [UU] unused devices: <none>
On this system, there are three RAID arrays (all RAID 1). Each RAID array has its own section in /proc/mdstat and contains the following information:
  • The RAID array device name (not including the /dev/ part)
  • The status of the RAID array
  • The RAID array's RAID level
  • The physical partitions that currently make up the array (followed by the partition's array unit number)
  • The size of the array
  • The number of configured devices versus the number of operative devices in the array
  • The status of each configured device in the array (U meaning the device is OK, and _ indicating that the device has failed)