我正在尝试使用 mdadm 创建一个软件 raid5 阵列：
$ 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.
但是在检查 /proc/mdstat 时
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>
似乎一个驱动器没有激活，所以我检查了阵列的详细信息：
/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
似乎只有 3 台活动设备，其中一台备用。
只是我，还是这里有问题？