Hello!

I have 3x2TB disks and I just bought fourth one. What would be steps to include new drive to existing array?

My setup is as follows (I think...):
1. Formatted all three drives to fd with fdisk
2. Created RAID5 array from these drives
3. Created LVM volume group from raid device
4. Created EXT4 filesystem for LVM volume group
5. Encrypted it with LUKS

This was some time ago and I did it with Fedora installer so I'm not 100% sure of those steps. Please correct me if I'm wrong.

OS is Slackware64-current and is up to date.

Your outlined steps contradicts your question. The steps are for new array, lvm and file system. Adding a new device would require different steps. See this link for setting up and modify RAID volumes.

Yes I know that those steps are for creating a new array. I was just trying to tell you how I have made the existing array.

Thanks for the link. I have to read it as soon as possible. I was wondering if LUKS encryption needs additional steps. This may sound stupid but I have really very little idea how it works.

The link is a RAID wiki and should answer all your questions. What you should keep in mind that you will need to increase the size starting will the lowest layer (typically, this is the physical devices).

If your setup is RAID5->LVM->LUKS->EXT4 you would:
1. Grow the RAID by increasing the number of devices
2. Resize the PV to the new RAID size and subsequently the LV(s).
3. Resize LUKS to the new LV size
4. Resize Ext4 to the new LV/LUKS size

If you have the order of LUKS and LVM switched, then adjust the steps accordingly.

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Thank you tux_dude!

The whole process went smoothly with your advice.