LinuxQuestions.org - RAID 5 with mdadm "spare" and "active sync" confusion

I am testing my RAID5 setup, and get confused on
"spare" and "active sync"

For md0, every drive has status "active sync", but md1 has one drive as "spare". I use the same mdadm cmd to build these 2 RAIDs, but not sure why it difference. My question is whether all 4 drives are used in the RAID array, or it indicates that one drive is failed. Any help would be great.

Code:

# mdadm --create /dev/md0 --level=raid5 --raid-devices=6 /dev/sdb[1-4] /dev/sde[1-2] 



# mdadm --create /dev/md1 --level=raid5 --raid-devices=4 /dev/sdc[1-2] /dev/sdc3 /dev/sdc5

Code:

# cat /proc/mdstat

Personalities : [raid0] [raid5]

md1 : active raid5 sdc5[4] sdc3[2] sdc2[1] sdc1[0]

      24121152 blocks level 5, 64k chunk, algorithm 2 [4/3] [UUU_]



md0 : active raid5 sdb2[1] sde2[5] sde1[4] sdb4[3] sdb3[2] sdb1[0]

      80364480 blocks level 5, 64k chunk, algorithm 2 [6/6] [UUUU

Here the output from

# mdadm --verbose --examine --scan

for md0 and md1 respectively

Code:

      



Number  Major  Minor  RaidDevice State

this    0      8      33        0      active sync  /dev/sdc1

  0    0      8      33        0      active sync  /dev/sdc1

  1    1      8      34        1      active sync  /dev/sdc2

  2    2      8      35        2      active sync  /dev/sdc3

  3    3      0        0        3      faulty removed

  4    4      8      37        4      spare  /dev/sdc5







      Number  Major  Minor  RaidDevice State

this    0      8      17        0      active sync  /dev/sdb1

  0    0      8      17        0      active sync  /dev/sdb1

  1    1      8      18        1      active sync  /dev/sdb2

  2    2      8      19        2      active sync  /dev/sdb3

  3    3      8      20        3      active sync  /dev/sdb4

  4    4      8      65        4      active sync  /dev/sde1

  5    5      8      66        5      active sync  /dev/sde2