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I have a Centos 7 system with 4 drives installed. They are setup in the bios as 2 mirrored pairs. When the system was installed, the default installation only saw one of the pairs and installed on it. I am now trying to figure out which drive to mount to gain access to the other drive pair. It appears from fdisk -l that drive sdc is the one Centos selected and sdd is the mirror. Thus, I should mount sda and sdb would be its mirror. But how can I tell for sure? Are they done in reverse somehow where sdd is primary and sdc the mirror, therefore I should mount sdb? Df -u doesn't seem to yield any clues.

df -h yields this...

Filesystem                                                          1K-blocks    Used Available Use% Mounted on 
/dev/mapper/centos-root    52403200 1269720  51133480   3% / 
devtmpfs                            3962440       0   3962440   0% /dev 
tmpfs                              3971896       0   3971896   0% /dev/shm 
tmpfs                          3971896    8872   3963024   1% /run 
tmpfs                              3971896       0   3971896   0% /sys/fs/cgroup 
/dev/mapper/centos-home  914001876  690184 913311692   1% /home 
/dev/mapper/ddf1_4c5349202020202080862925000000004711471100001e78p1    508588  167460    341128  33% /boot

And this is fdisk -l

Disk /dev/sda: 1000.2 GB, 1000204886016 bytes, 1953525168 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/sdb: 1000.2 GB, 1000204886016 bytes, 1953525168 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/sdc: 1000.2 GB, 1000204886016 bytes, 1953525168 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: 0x000bd18a

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1   *        2048     1026047      512000   83  Linux
/dev/sdc2         1026048  1951170559   975072256   8e  Linux LVM

Disk /dev/sdd: 1000.2 GB, 1000204886016 bytes, 1953525168 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: 0x000bd18a

   Device Boot      Start         End      Blocks   Id  System
/dev/sdd1   *        2048     1026047      512000   83  Linux
/dev/sdd2         1026048  1951170559   975072256   8e  Linux LVM

Disk /dev/mapper/ddf1_4c5349202020202080862925000000004711471100001e78: 999.0 GB, 998999326720 bytes, 1951170560 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: 0x000bd18a

                                                             Device Boot      Start         End      Blocks   Id  System
/dev/mapper/ddf1_4c5349202020202080862925000000004711471100001e78p1   *        2048     1026047      512000   83  Linux
/dev/mapper/ddf1_4c5349202020202080862925000000004711471100001e78p2         1026048  1951170559   975072256   8e  Linux LVM

Disk /dev/mapper/ddf1_4c5349202020202080862925000000004711471100001e78p1: 524 MB, 524288000 bytes, 1024000 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/ddf1_4c5349202020202080862925000000004711471100001e78p2: 998.5 GB, 998473990144 bytes, 1950144512 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: 8321 MB, 8321499136 bytes, 16252928 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-root: 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


Disk /dev/mapper/centos-home: 936.4 GB, 936395145216 bytes, 1828896768 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/ddf1_4c53492020202020808629250000000047114711000028a0: 999.0 GB, 998999326720 bytes, 1951170560 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
Doug Wolfgram
  • 113

1 Answers1

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Considering your drives are in mirror, you don't access them directly (using /dev/sd*), instead, you use the /dev/mapper/ddf* device.

You have two ddf devices:

  1. /dev/mapper/ddf1_4c53492020202020808629250000000047114711000028a0 out of /dev/sda and /dev/sdb
  2. /dev/mapper/ddf1_4c5349202020202080862925000000004711471100001e78 out of /dev/sdc and /dev/sdd

/dev/mapper/ddf1_4c5349202020202080862925000000004711471100001e78 has two partitions, /dev/mapper/ddf1_4c5349202020202080862925000000004711471100001e78p1 and /dev/mapper/ddf1_4c5349202020202080862925000000004711471100001e78p2, second one being your LVM volume for /dev/mapper/centos-swap, /dev/mapper/centos-root and /dev/mapper/centos-home.

So the drive you are looking for is /dev/mapper/ddf1_4c53492020202020808629250000000047114711000028a0. You have to partition in and stuff :)

petry
  • 978
  • Is mounting the same? When I look in fstab I don't see /dev/mapper/ddf1_4c5349202020202080862925000000004711471100001e78 anywhere... – Doug Wolfgram Oct 28 '15 at 09:25
  • @DougWolfgram you can not directly mount /dev/mapper/ddf1_4c5349202020202080862925000000004711471100001e78 (the same way you don't mount /dev/sda). You have to partition it first, so you'll have something like /dev/mapper/ddf1_4c5349202020202080862925000000004711471100001e78p1, and get a filesystem on that partition. – petry Oct 28 '15 at 09:34
  • Ugh. I just want one large partition for /data. Ho do I do that? I've been adminning linux for years but never dealt with morrored pairs. :) – Doug Wolfgram Oct 28 '15 at 09:38
  • @DougWolfgram just fdisk /dev/mapper/ddf1_4c53492020202020808629250000000047114711000028a0 as you would do with any drive, add only one partition (should be something like /dev/mapper/ddf1_4c53492020202020808629250000000047114711000028a0p1, mkfs on it, and add it in /etc/fstab/. – petry Oct 28 '15 at 09:51