linux – 如何创建一个没有备用的软件raid5数组

我正在尝试使用mdadm创建一个软件raid5数组：

$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>

似乎一个驱动器不活动,所以我检查数组的详细信息：

/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

而且似乎只有3个有源设备,只有一个备用设备.

这只是我,还是错在这里？

解决方法

This tutorial涵盖了使用mdadm构建raid5数组.您不能在少于三台设备的情况下使用raid5.

你是什​​么意思？ Raid5旨在提供冗余以应对一台设备的故障.如果不这样做那么它就不再是raid5了.

问题编辑后编辑：

When creating a RAID5 array,mdadm will automatically create a degraded
   array with an extra spare drive.  This is because  building  the  spare
   into a degraded array is in general faster than resyncing the parity on
   a non-degraded,but not clean,array.  This feature can  be  overridden
   with the --force option.

这似乎就是这样,mdadm将新阵列设置为使用备用降级,然后将备用数据放入以构建阵列.