Join Several Partition Together To Form a Single Larger One On a Linux Using mhddfs

The easiest and fastest solution is to use mhddfs driver on Linux operating systems. It is a fuse-based file system for unifying several mount points into one. 

The mhddfs (fuse) file system allows to unite a several mount points (or directories) to the single one. So a one big filesystem is simulated and this makes it possible to combine a several hard drives or network file systems. This system is like unionfs but it can choose a drive with the most of free space, and move the data between drives transparently for the applications. While writing files they are written to a 1st hdd until the hdd has the free space (see mlimit option), then they are written on a 2nd hdd, then to 3rd etc. df will show a total statistics of all filesystems like there is a big one hdd. If an overflow arises while writing to the hdd1 then a file content already written will be transferred to a hdd containing enough of free space for a file. The transferring is processed on-the-fly, fully transparent for the application that is writing. So this behaviour simulates a big file system.

In this tutorial you will learn how to install and configure MHDDFS virtual storage pool on a Linux operating systems.

Our sample setup
For demo purpose I’ve three hard disks drive /dev/sdb1, /dev/sdc1, and /dev/sdd1 as follows:

# df

Sample outputs:

And files in my /disk{1,2,3}/ dirs are as follows:

# ls -l /disk{1,2,3}

Sample outputs: 

/disk1:
total 28
drwxr-xr-x 2 root root 4096 Aug 8 14:25 app1
drwx------ 2 root root 16384 Aug 8 14:20 lost+found
-rw-r--r-- 1 root root 7545 Aug 8 14:26 resume.txt

/disk2:
total 28
drwxr-xr-x 2 root root 4096 Aug 8 14:25 app2
drwx------ 2 root root 16384 Aug 8 14:20 lost+found
-rw-r--r-- 1 root root 6303 Aug 8 14:26 party.jpg

/disk3:
total 40
drwxr-xr-x 2 root root 4096 Aug 8 14:25 app3
drwx------ 2 root root 16384 Aug 8 14:21 lost+found
-rw-r--r-- 1 root root 17080 Aug 8 14:26 output.log

Installation

Install mhddfs package on a Debian/Ubuntu/Mint Linux & Co. Type the following apt-get command to install mhddfs:

# apt-get install mhddfs

Sample outputs:

Install mhddfs package on a Fedora/RHEL/CentOS Linux & Co Turn on EPEL repo and type the following command:

# yum install mhddfs

Fedora Linux v22.x+ user type the following command:

# dnf install mhddfs

Configuration

First, create a new mount point directory called /virtual.data, enter:

# mkdir /virtual.data

To join all three drives (see fig.01) together, enter:

# mhddfs /disk1,/disk2,/disk3 /virtual.data -o allow_other

Sample outputs:

That’s all. You can now verify that /virtual.data/ as a single bing volume i.e. several directories combined, simulating a single big volume which can merge several hard drives or remote file systems:

# df

Sample outputs: 

Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda1 39428520 6109320 31293268 17% /
udev 10240 0 10240 0% /dev
tmpfs 811792 9084 802708 2% /run
tmpfs 2029472 144 2029328 1% /dev/shm
tmpfs 5120 4 5116 1% /run/lock
tmpfs 2029472 0 2029472 0% /sys/fs/cgroup
tmpfs 405896 16 405880 1% /run/user/1000
/dev/sdb1 4061888 8196 3827644 1% /disk1
/dev/sdc1 4061888 8196 3827644 1% /disk2
/dev/sdd1 4061888 8208 3827632 1% /disk3
/disk1;/disk2;/disk3 12185664 24600 11482920 1% /virtual.data

Also, note down ls -l command output:

# ls -l /virtual.data/
total 64
drwxr-xr-x 2 root root 4096 Aug 8 14:25 app1
drwxr-xr-x 2 root root 4096 Aug 8 14:25 app2
drwxr-xr-x 2 root root 4096 Aug 8 14:25 app3
drwx------ 2 root root 16384 Aug 8 14:20 lost+found
-rw-r--r-- 1 root root 17080 Aug 8 14:26 output.log
-rw-r--r-- 1 root root 6303 Aug 8 14:26 party.jpg
-rw-r--r-- 1 root root 7545 Aug 8 14:26 resume.txt

You can now copy files or create new directories as per your requirement:

# cd /virtual.data/
# mkdir Music
# rsync -avp /somewhere/* Music/
....
..

Update /etc/fstab file as follows:

mhddfs#/disk1,/disk2,disk3 /virtual.data/ fuse defaults,allow_other 0 0

How do I unmount mhddfs based fuse file systems

Use the umount command to detaches the /virtual.data/ file system:

# umount /virtual.data/

For more info type see mhddfs man page.

Src: https://www.cyberciti.biz/faq/mhddfs-linux-combines-a-several-mount-points-into-single-one/