====== RAID - mdadm - Check the RAID status ======

<code bash>
cat /proc/mdstat
</code>

returns:

<code bash>
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] [multipath] 
md0 : active raid6 sdf3[0] sdd3[7] sdg3[6] sdh3[5] sdc3[4] sdb3[2] sda3[3] sde3[1]
      46824429696 blocks super 1.0 level 6, 64k chunk, algorithm 2 [8/8] [UUUUUUUU]
      bitmap: 21/59 pages [84KB], 65536KB chunk
</code>

<WRAP info>
**NOTE:**

  * **Personalities**:  What RAID levels the kernel currently supports.
    * This can be changed by either changing the raid modules or recompiling the kernel.
    * Possible personalities include: [raid0] [raid1] [raid4] [raid5] [raid6] [linear] [multipath] [faulty] 
      * **[faulty]** is a diagnostic personality; it does not mean there is a problem with the array.

  * **md0**:  The device is /dev/md0.
  * **active**:  The RAID is active and started.
    * An inactive array is usually faulty. Stopped arrays are not visible here.
  * **raid6**:  The type of RAID array and the component devices are:
    * **sdf3[0]** is device 0.
    * **sdd3[7]** is device 7.
    * **sdg3[6]** is device 6.
    * **sdh3[5]** is device 5.
    * **sdc3[4]** is device 4.
    * **sdb3[2]** is device 2.
    * **sda3[3]** is device 3.
    * **sde3[1]** is device 1.
      * The order in which the devices appear in this line means nothing.
  * **46824429696 blocks**:  The usable size of the array in blocks.
  * **super 1.0**:  The array uses a 1.0 [[https://raid.wiki.kernel.org/index.php/RAID_superblock_formats|superblock]].
  * **level 6**:  Confirms this is a level 6 array.
  * **64k chunk**:  Has a chunk size of 64k.
    * This is the size for 'chunks' and is only relevant to raid levels that involve striping (1,4,5,6,10).
    * The address space of the array is conceptually divided into chunks and consecutive chunks are striped onto neighboring devices. 
  * **algorithm 2**:  Uses algorithm 2.
  * **[8/8]**:  The first number is the number of a complete raid devices as defined.  The second number is how many devices are in use.
  * **[UUUUUUUU]**:  The status of each device.
    * **F**:  The drive has failed.
    * **U**:  The drive is used and working fine.
    * **_**:  The drive is down.

</WRAP>


----

<code bash>
mdadm --detail /dev/md1
</code>

returns:

<code bash>
/dev/md1:
        Version : 1.0
  Creation Time : Tue Mar  6 17:46:54 2018
     Raid Level : raid6
     Array Size : 46824429696 (44655.26 GiB 47948.22 GB)
  Used Dev Size : 7804071616 (7442.54 GiB 7991.37 GB)
   Raid Devices : 8
  Total Devices : 8
    Persistence : Superblock is persistent

  Intent Bitmap : Internal

    Update Time : Tue Sep 14 00:02:02 2021
          State : active 
 Active Devices : 8
Working Devices : 8
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 64K

           Name : 1
           UUID : 85d45e53:913fde8a:55ba7e06:ee932838
         Events : 16304341

    Number   Major   Minor   RaidDevice State
       0       8       83        0      active sync   /dev/sdf3
       1       8       67        1      active sync   /dev/sde3
       3       8        3        2      active sync   /dev/sda3
       2       8       19        3      active sync   /dev/sdb3
       4       8       35        4      active sync   /dev/sdc3
       5       8      115        5      active sync   /dev/sdh3
       6       8       99        6      active sync   /dev/sdg3
       7       8       51        7      active sync   /dev/sdd3
</code>

----