Adding a New Hard Drive

Adding a new hard drive to a Linux instance involves the following steps

• Add physical / virtual drive to the instance
• Scan for and identify new drive
• Prepare new drive for use

Adding the new drive is outside of the scope of this article, as it can be done in many different ways depending on the instance – either a new physical disk needs to be added, or a virtual drive created using your virtual machine hypervisor GUI or Cloud console added to the virtual machine.

Scanning for the new drive

After the new drive has been added to the instance, it needs to be presented to the operating system for configuration. There are two ways of doing this, by either rebooting the instance or by scanning all of the drive busses for new devices.

# ls -1 /sys/class/scsi_host/*/scan
/sys/class/scsi_host/host0/scan
/sys/class/scsi_host/host1/scan
/sys/class/scsi_host/host2/scan
/sys/class/scsi_host/host3/scan
# for i in `ls /sys/class/scsi_host/*/scan`; do echo "- - -" > ${i}; done

Once the new drive has been recognised by the operating system, it should be visible to the lsblk statement – in this example it is sdb which we can see has no partitions defined. It’s best to have an example of the following output before adding the drive for comparison.

# lsblk
NAME                      MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
loop0                       7:0    0 88.5M  1 loop /snap/core/7270
loop1                       7:1    0 89.1M  1 loop /snap/core/8268
sda                         8:0    0   10G  0 disk
├─sda1                      8:1    0    1M  0 part
├─sda2                      8:2    0    1G  0 part /boot
└─sda3                      8:3    0    9G  0 part
  └─ubuntu--vg-ubuntu--lv 253:0    0    4G  0 lvm  /
sdb                         8:16   0   10G  0 disk
sr0                        11:0    1 1024M  0 rom

Preparing the new drive for use

Now that the new drive has been presented to the operating system and is accessible, we need to make the drive available for use. I find that the best and most flexible way to use this new drive is to allocate all of the drive to the logical volume manager LVM – do this by first creating the new physical volume

# pvcreate /dev/sdb
  Physical volume "/dev/sdb" successfully created.

Once the physical volume has been recognised by the operating system, we can either create a new volume group as shown below, or add this new physical volume to an existing volume group.

# vgcreate data-vg /dev/sdb
  Volume group "data-vg" successfully created

The next step is to create a new logical volume or extend an existing logical volume. You can only extend a logical volume if you have extended the volume group it belongs to.

# lvcreate -l 100%FREE -n data data-vg
  Logical volume "data" created.

Which will create a new logical volume called data inside the data-vg volume group. The details for this new logical volume can be displayed with the lvdisplay command

# lvdisplay /dev/data-vg/data
  --- Logical volume ---
  LV Path                /dev/data-vg/data
  LV Name                data
  VG Name                data-vg
  LV UUID                Fv1q0Y-F1Bt-HLBY-sKWk-svvJ-W9WE-eMasO5
  LV Write Access        read/write
  LV Creation host, time abd-template, 2019-12-27 16:39:00 +0000
  LV Status              available
  # open                 0
  LV Size                <10.00 GiB
  Current LE             2559
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1

The new logical volume can be formatted with a filesystem, and for most general applications the ext4 filesystem is well suited

# mkfs.ext4 /dev/data-vg/data
mke2fs 1.44.1 (24-Mar-2018)
Creating filesystem with 2620416 4k blocks and 655360 inodes
Filesystem UUID: 018b2220-6e10-4f46-9f06-233b68acf4f3
Superblock backups stored on blocks:
	32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632

Allocating group tables: done
Writing inode tables: done
Creating journal (16384 blocks): done
Writing superblocks and filesystem accounting information: done

Then mount the new volume to the filesystem – by adding an entry to the /etc/fstab file, we can ensure this volume is automatically mounted after a reboot

# mkdir /data
# echo "/dev/data-vg/data   /data   ext4  defaults  0  0" >> /etc/fstab
# mount /data
# df /data
Filesystem                1K-blocks  Used Available Use% Mounted on
/dev/mapper/data--vg-data  10251540 36888   9674188   1% /data

The new drive is now available to the operating system under the /data path.

In summary, the commands required are as follows, assuming you are adding the drive sdb and creating the logical volume /dev/data-vg/data

for i in `ls /sys/class/scsi_host/*/scan`; do echo "- - -" > ${i}; done
pvcreate /dev/sdb
vgcreate data-vg /dev/sdb
lvcreate -l 100%FREE -n data data-vg
mkfs.ext4 /dev/data-vg/data
mkdir /data
echo "/dev/data-vg/data   /data   ext4  defaults  0  0" >> /etc/fstab
mount /data