/home /opt /tmp /usr /var on a single partition of another hard drive Debian 8

Question

I have a production server for which I would like to move the /home, /opt, /tmp, /user, /var to the ~300GB partition specially created for this purpose.

No straightforward explanation found on how to do this, except that I can put every folder specified above on a separate partition, but I don't want to do that. Reasons:

1. I don't know how much space these folders might use in the end, so one drive with all of it will do nicely.
2. I see it much simpler for me. I don't want to have tons of partitions on the same drive.
3. I will install a server app, that will do much I/O and a MySQL server, and I don't want it to slow down the system hard drive or interfere with it.
4. Intelligent partitioning

Is there any way to achieve what I want, so all would work as if the folders are on the same hard drive?

P.S. These are the most rellevant links I've found so far:

Link1_LinuxAndUnix

Link2_UbuntuDocumentation

Link3_LinuxNewbieAdministrator

Thank you!

UPDATE:

All mounted!

UUID=rootUUID / ext4 errors=remount-ro 0 1
UUID=swapUUID none swap sw 0 0
/dev/sr0 /media/cdrom0 udf,iso9660 user,noauto 0 0
UUID=otherDriveUUID /mnt/sdb2 ext4 defaults 0 1
/mnt/sdb2/tmp /tmp none defaults,bind 0 2
/mnt/sdb2/local /usr/local none defaults,bind 0 2
/mnt/sdb2/home /home none defaults,bind 0 2
/mnt/sdb2/opt /opt none defaults,bind 0 2
/mnt/sdb2/var /var none defaults,bind 0 2

Answer 1

What you're looking for is bind mounts. See http://man7.org/linux/man-pages/man8/mount.8.html for details.

Here is a step by step guide to moving /home, /opt, /tmp, /usr, and /var to a single separate partition.

Disclaimer

I am not responsible for any damage or loss of data caused by following this guide. As always, ensure all important data is backed up before proceeding.

Step 1

Boot from your favourite live CD. Example: https://www.debian.org/CD/live/

Switch to root shell. This can often be done with sudo su -

Step 2

Mount your primary and secondary partitions. We'll assume that they are /dev/sda1 and /dev/sdb1 for the purpose of this guide.

mkdir /mnt/sd{a,b}1
mount /dev/sda1 /mnt/sda1
mount /dev/sdb1 /mnt/sdb1

Step 3

Move existing folders/data from primary to secondary partition. This may take a few minutes depending on the size of the folders and speed of your drives.

mv /mnt/sda1/{home,opt,tmp,usr,var} /mnt/sdb1/

Step 4

Create empty folders on the primary partition to give us mount points.

mkdir /mnt/sda1/{home,opt,tmp,usr,var} /mnt/sda1/mnt/sdb1

Step 6

Edit your fstab to automatically mount the secondary partition and bind mount the appropriate folders. This step is largely subjective to your current configuration and may not work as a direct copy/paste.

Edit /mnt/sda1/etc/fstab with your favourite editor.

You can find detailed information on the fstab at http://man7.org/linux/man-pages/man5/fstab.5.html

First we need to mount the secondary partition before we can bind mount to it. This partition may already be in your fstab. If so, edit/remove the configuration accordingly. Here, we'll assume it's an ext4 partition with default options.

/dev/sdb1 /mnt/sdb1 ext4 defaults 0 2

Next, configure the bind mounts.

/mnt/sdb1/home /home none defaults,bind 0 0
/mnt/sdb1/opt /opt none defaults,bind 0 0
/mnt/sdb1/tmp /tmp none defaults,bind 0 0
/mnt/sdb1/usr /usr none defaults,bind 0 0
/mnt/sdb1/var /var none defaults,bind 0 0

Save your changes to the fstab.

Step 7

Reboot