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Recently we configured an Ubuntu 16.04 on Server. We have two 256 GBs SSDs. After a while we recognised that our main RAID partition has only 20GBs while other partition has more than 200GBs.

Here's what fdisk -l prints out:

Disk /dev/sda: 238.5 GiB, 256060514304 bytes, 500118192 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
Disklabel type: dos
Disk identifier: 0x807adac1

Device     Boot    Start       End   Sectors   Size Id Type
/dev/sda1  *        2048    614399    612352   299M fd Linux raid autodetect
/dev/sda2         614400   1662975   1048576   512M 82 Linux swap / Solaris
/dev/sda3        1662976  43606015  41943040    20G fd Linux raid autodetect
/dev/sda4       43606016 500117503 456511488 217.7G fd Linux raid autodetect


Disk /dev/sdb: 238.5 GiB, 256060514304 bytes, 500118192 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
Disklabel type: dos
Disk identifier: 0x9a57a62a

Device     Boot    Start       End   Sectors   Size Id Type
/dev/sdb1  *        2048    614399    612352   299M fd Linux raid autodetect
/dev/sdb2         614400   1662975   1048576   512M 82 Linux swap / Solaris
/dev/sdb3        1662976  43606015  41943040    20G fd Linux raid autodetect
/dev/sdb4       43606016 500117503 456511488 217.7G fd Linux raid autodetect


Disk /dev/md0: 298.7 MiB, 313196544 bytes, 611712 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/md2: 217.6 GiB, 233599664128 bytes, 456249344 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/md1: 20 GiB, 21458059264 bytes, 41910272 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

The problem is we run out of space everytime we want to install or run something new on /dev/md1 which is our main partition.

Question is though, how can we run away from this? Is there a way to use /dev/md2 beside /dev/md1 so that we don't encounter low space disk issues or even shrink /dev/md2 and grow /dev/md1?

We followed so many tutorials but no luck resizing /dev/md1.

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The recommended way to avoid the space problem in your situation is to move existing directories to the filesystem in /dev/md2, and use symlinks to point to the new directory.

Resizing the MD device is a more complex process:

  1. Copy all contents of /dev/md2 to another place
  2. Delete the /dev/md2 device and partitions /dev/sda4 and /dev/sdb4 which are the RAID members.
  3. Increase the size of /dev/sda3 and /dev/sdb3 partitions to the size you want.
  4. Use mdadm --grow to increase the size of /dev/md1 to match the size of underlying partitions.
  5. Re-create /dev/sda4 and /dev/sdb4 partitions and create RAID array on top of them.
  6. Copy the data back to the partitions.

The reason why you have to do all of this is because the MD devices consist of disk partitions, and partitions are single areas in the hard disk. Therefore, you have to free the space after the partition in order to increase it.

Increasing the size of filesystems would be easier if there was Logical Volume Manager (LVM) in use.

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  • It looks like software mdadm RAID1. Is there no dedicated RAID controller on the server? Please provide more details. Unfortunately, there is no easy way to modify this setup and this always be a risky operation as @TeroKilkanen wrote. But for me this is very unelastic setup for a server. My recommendation is to reinstall the system with LVM; this way you will have much needed freedom to safely modify your setup. K.
    – kmwil
    Jul 23 '17 at 7:37

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