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brad
Asked: 2020-10-23 17:06:28 +0800 CST

Can I combine physical drives into a single volume for use as part of a RAID?

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I have a home media server that currently has 4 4TB drives in a Raid5 using mdadm. This gives me 12TB of space currently and it has almost run out. I want to add more space but would like to use bigger drives. I plan to eventually have 3 12TB drives in a Raid5, but don’t want to spend that much in one go.

I am wondering if the following pathway if feasible;

  1. Purchase and install a single 12TB drive and create an 8TB partition and a 4TB partition.
  2. Copy 8TB of my existing data to the 8 TB partition and the remaining 4TB to the new 4TB partition.
  3. Use LVM to combine the 4TB drives into 2 8TB logical volumes.
  4. Use mdadm to combine my one physical 8TB and 2 logical 8TB volumes into a 16TB RAID5 array (preserving the data on the physical 8TB drive).
  5. Copy the 4TB of data on the other partition into the new RAID volume leaving me with 4TB of space.
  6. When I get close to filling this (likely to be over a year or more from now) buy 2 new 12TB drives, create 8TB partitions on each, move the RAID to the 3 12TB drives, then grow the partitions to 12TB creating a 24TB RAID5 drive

Will this work?

Anyone got a smarter way of doing this that doesn’t involve just buying 3 drives right now?

raid mdadm raid5

1 Answers

  1. Best Answer

    Well, this didn't get a lot of activity or interest, but I went ahead and tried it. The answer is, yes this works. Took several days of RAID grinding to get there. Here is the proof (after step 4).

    $ sudo lsblk
NAME                 MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
loop0                  7:0    0  97.8M  1 loop  /snap/core/10185
loop1                  7:1    0  97.7M  1 loop  /snap/core/10126
loop2                  7:2    0  55.4M  1 loop  /snap/core18/1932
loop3                  7:3    0  69.2M  1 loop  /snap/lxd/18077
loop4                  7:4    0  69.2M  1 loop  /snap/lxd/18137
loop5                  7:5    0  55.3M  1 loop  /snap/core18/1885
sda                    8:0    0   3.7T  0 disk  
└─sda1                 8:1    0   3.7T  0 part  
  └─8tbraidvol1-vol1 253:0    0   7.3T  0 lvm   
    └─md127            9:127  0  14.6T  0 raid5 /mnt/raid
sdb                    8:16   0   3.7T  0 disk  
└─sdb1                 8:17   0   3.7T  0 part  
  └─8tbraidvol1-vol1 253:0    0   7.3T  0 lvm   
    └─md127            9:127  0  14.6T  0 raid5 /mnt/raid
sdc                    8:32   0   3.7T  0 disk  
└─sdc1                 8:33   0   3.7T  0 part  
  └─8tbraidvol2-vol2 253:1    0   7.3T  0 lvm   
    └─md127            9:127  0  14.6T  0 raid5 /mnt/raid
sdd                    8:48   0   3.7T  0 disk  
└─sdd1                 8:49   0   3.7T  0 part  
  └─8tbraidvol2-vol2 253:1    0   7.3T  0 lvm   
    └─md127            9:127  0  14.6T  0 raid5 /mnt/raid
sde                    8:64   1  10.9T  0 disk  
├─sde1                 8:65   1   7.3T  0 part  
│ └─md127              9:127  0  14.6T  0 raid5 /mnt/raid
└─sde2                 8:66   1   3.7T  0 part  /mnt/spare
sr0                   11:0    1  1024M  0 rom   
nvme0n1              259:0    0 465.8G  0 disk  
├─nvme0n1p1          259:1    0   512M  0 part  /boot/efi
└─nvme0n1p2          259:2    0 465.3G  0 part  /

$ sudo df -h
Filesystem      Size  Used Avail Use% Mounted on
udev             16G     0   16G   0% /dev
tmpfs           3.2G  4.2M  3.2G   1% /run
/dev/nvme0n1p2  457G  129G  305G  30% /
tmpfs            16G     0   16G   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs            16G     0   16G   0% /sys/fs/cgroup
/dev/nvme0n1p1  511M  7.8M  504M   2% /boot/efi
/dev/loop1       98M   98M     0 100% /snap/core/10126
/dev/loop0       98M   98M     0 100% /snap/core/10185
/dev/loop2       56M   56M     0 100% /snap/core18/1932
/dev/loop3       70M   70M     0 100% /snap/lxd/18077
/dev/loop5       56M   56M     0 100% /snap/core18/1885
/dev/loop4       70M   70M     0 100% /snap/lxd/18137
tmpfs           3.2G     0  3.2G   0% /run/user/1000
/dev/md127       15T  6.8T  7.0T  50% /mnt/raid
/dev/sde2       3.6T  3.3T  109G  97% /mnt/spare
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