I am trying to create a software raid5 array using mdadm:
$ linux # mdadm --create --verbose /dev/md0 --level=5 --raid-devices=4 --spare-devices=0 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1
mdadm: layout defaults to left-symmetric
mdadm: chunk size defaults to 64K
mdadm: array /dev/md0 started.
However when inspecting /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 sdd1[4] sdc1[2] sdb1[1] sda1[0]
2930279808 blocks level 5, 64k chunk, algorithm 2 [4/3] [UUU_]
[>....................] recovery = 0.3% (2970496/976759936) finish=186.1min speed=87172K/sec
unused devices: <none>
It seems one drive isn't active, so I check the details of the array:
/dev/md0:
Version : 00.90.03
Creation Time : Tue Jul 21 16:29:53 2009
Raid Level : raid5
Array Size : 2930279808 (2794.53 GiB 3000.61 GB)
Used Dev Size : 976759936 (931.51 GiB 1000.20 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Tue Jul 21 16:29:53 2009
State : clean, degraded, recovering
Active Devices : 3
Working Devices : 4
Failed Devices : 0
Spare Devices : 1
Layout : left-symmetric
Chunk Size : 64K
Rebuild Status : 0% complete
UUID : ce8b2f40:821d003c:0027688e:a70977ec
Events : 0.1
Number Major Minor RaidDevice State
0 8 1 0 active sync /dev/sda1
1 8 17 1 active sync /dev/sdb1
2 8 33 2 active sync /dev/sdc1
4 8 49 3 spare rebuilding /dev/sdd1
And it seems there are only 3 active devices, with one spare.
Is it just me, or something wrong here?