Two hard drives each with software RAID1 on CentOS 7?

Aren Tahmasian asked:

Disclaimer: I did not create this server.

From what I see below, it seems as if I have two identical drives, /dev/sda and /dev/sdb, and each one has its own software RAID1. Am I completely reading this wrong? The server does support hardware RAID1 but the hardware RAID1 should not be visible in the commands below. And the fact that I’m seeing /dev/mdX means there’s a software RAID present. Does each drive have it’s own software RAID1?

This is the output of lsblk -o name,fstype,maj:min,size,type,mountpoint,uuid

NAME                   FSTYPE         MAJ:MIN   SIZE   TYPE  MOUNTPOINT UUID
sda                    isw_raid_mem   8:0       465.8G disk             
└─md126                               9:126     442.5G raid1            
  ├─md126p1            xfs            259:0     1G     md    /boot      f178f32e-b423-4000-b458-1a2e9c36a295
  └─md126p2            LVM2_member    259:1     441.5G md               VXBriv-sYp5-AZyT-UrI1-uzDt-Bjkw-ZI1Ka5
    ├─centos_root      xfs            253:0     350G   lvm   /          3b2a2d46-e097-44b5-98a7-24256a047bbb
    ├─centos_swap      swap           253:1     41.5G  lvm   [SWAP]     b0ca8a53-f78b-4afd-b0fc-6b86a47e59aa
    └─centos_home      xfs            253:2     50G    lvm   /home      4cb3b128-ccb7-41b5-af2c-abc0a9b54112
sdb                    isw_raid_mem   8:16      465.8G disk             
└─md126                               9:126     442.5G raid1            
  ├─md126p1            xfs            259:0     1G     md    /boot      f178f32e-b423-4000-b458-1a2e9c36a295
  └─md126p2            LVM2_member    259:1     441.5G md               VXBriv-sYp5-AZyT-UrI1-uzDt-Bjkw-ZI1Ka5
    ├─centos_root      xfs            253:0     350G   lvm   /          3b2a2d46-e097-44b5-98a7-24256a047bbb
    ├─centos_swap      swap           253:1     41.5G  lvm   [SWAP]     b0ca8a53-f78b-4afd-b0fc-6b86a47e59aa
    └─centos_home      xfs            253:2     50G    lvm   /home      4cb3b128-ccb7-41b5-af2c-abc0a9b54112

Here is the output of /proc/mdstat

Personalities : [raid1] 
md126 : active raid1 sda[1] sdb[0]
      463992832 blocks super external:/md127/0 [2/2] [UU]

md127 : inactive sdb[1](S) sda[0](S)
      6306 blocks super external:imsm

unused devices: <none>

Here is the output of /etc/mdadm.conf

# mdadm.conf written out by anaconda
MAILADDR root
AUTO +imsm +1.x -all
ARRAY /dev/md/Volume0_0 UUID=81677824:f064e89e:eec139df:de40c0e5
ARRAY /dev/md/imsm0 UUID=58987cc8:398c9863:db0f4339:3f35e11c

Output of mdadm --detail /dev/md126

/dev/md126:
         Container : /dev/md/imsm0, member 0
        Raid Level : raid1
        Array Size : 463992832 (442.50 GiB 475.13 GB)
     Used Dev Size : 463992964 (442.50 GiB 475.13 GB)
      Raid Devices : 2
     Total Devices : 2

             State : clean 
    Active Devices : 2
   Working Devices : 2
    Failed Devices : 0
     Spare Devices : 0

Consistency Policy : resync


              UUID : 81677824:f064e89e:eec139df:de40c0e5
    Number   Major   Minor   RaidDevice State
       1       8        0        0      active sync   /dev/sda
       0       8       16        1      active sync   /dev/sdb

Output of fdisk -l

Disk /dev/sda: 500.1 GB, 500107862016 bytes, 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000b2b72

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048     2099199     1048576   83  Linux
/dev/sda2         2099200   927985663   462943232   8e  Linux LVM

Disk /dev/sdb: 500.1 GB, 500107862016 bytes, 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000b2b72

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *        2048     2099199     1048576   83  Linux
/dev/sdb2         2099200   927985663   462943232   8e  Linux LVM

Disk /dev/md126: 475.1 GB, 475128659968 bytes, 927985664 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000b2b72

      Device Boot      Start         End      Blocks   Id  System
/dev/md126p1   *        2048     2099199     1048576   83  Linux
/dev/md126p2         2099200   927985663   462943232   8e  Linux LVM

Disk /dev/mapper/centos_root: 375.8 GB, 375809638400 bytes, 734003200 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/mapper/centos_swap: 44.6 GB, 44551897088 bytes, 87015424 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/mapper/centos_home: 53.7 GB, 53687091200 bytes, 104857600 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

My answer:


You have two identical drives. But you have only one RAID1, which uses each of those two drives as mirror members. The RAID array uses Intel fake RAID, not true hardware RAID.


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