How to create/add swap space using a storage device?

Environment

• Red Hat Enterprise Linux (RHEL) 5, 6, 7, 8, 9, 10

Issue

• How to create swap space after installing the OS?
• Is it possible to create swap space on SAN disks using lvm ?
• Is it possible to create swap space on LVM disk in Red Hat Enterprise Linux?
• How to create swap space on LVM partition after installation of Red Hat Enterprise Linux?
• How to add additional swap device after OS installation.

• Exceptions:
• For creating a filesystem file for swap:
• Follow the directions in: "How do I add swap using a filesystem file to my Red Hat Enterprise Linux system?"

Resolution

• The procedure to create swap space after installation on SAN LUNs is similar to that on internal disk. It is possible to create swap space on a SAN disk using lvm.
  1. prepare the swap device, if needed
  2. create (format) the swap device
  3. add the swap device to /etc/fstab
  4. activate the swap device
  5. verify activated swap includes device

Note  If you have trouble creating and adding a swap device, capture the following diagnostics to submit to Red Hat along with a support case:

# hexdump -n 65536 -C <swap-device-name>  > hexdump.log  # for example /dev/mapper/mpath22p1 
# strace -v swapon -va &> swapon.log
# cat /etc/fstab &> fstab.log

Refer following steps to create swap space on the LVM partition, assuming for example that /dev/VolGroup00/LogVol02 is the swap volume to add:

1. Create the LVM logical volume, for example with 1GB (-L 1G). VolGroup00 is the vg name in which the LV LogVol02 is being created:

   # lvcreate VolGroup00 -n LogVol02 -L 1G
   

2. Format the new swap space:

   # mkswap /dev/VolGroup00/LogVol02
   

3. Add the following entry to the /etc/fstab file:

   /dev/VolGroup00/LogVol02 swap swap defaults 0 0
   

4. Enable the extended logical volume as swap:

   # swapon -va
   

5. To test if the swap space was successfully created, execute one of the following commands:

      # swapon -s
   
      # cat /proc/swaps
           
       or
           
      # free
   

The steps for using a physical device like sdX or multipath device is mostly the same steps.

• Refer following steps to create swap space on a device or device's partition, assuming for example that /dev/mapper/mpath22p1 is the swap device to be added. If the device was a local device /dev/sdx or a partition /dev/sdx1 then just substitute that for /dev/mapper/mpath22p1.

1. Verify the device, partition and/or multipath device is present within the configuration and not used.
    
2. Format the new `swap` space:

   # mkswap /dev/mapper/mpath22p1

3. Add the following entry to the `/etc/fstab` file:

   Note  If the device added to fstab is a sdX path under a multipath device, then attempting to activate with swapon will fail with 'invalid device' error -- you must specify the multipath device name, or its dm- equivalent, if adding swap using a multipath device.

   /dev/mapper/mpath22p1 swap swap defaults 0 0

4. Enable the device as swap:

   # swapon -va

5. To test if the swap space was successfully created, execute one of the following commands:

   # swapon -s
   
   # cat /proc/swaps
    
   
   or
    
   
   # free
   

Additional References

Although the following are located within the RHEL 8 documentation set, these steps are still valid for RHEL prior releases back to RHEL 5. For example, compare RHEL 5 with RHEL 8 for "Creating an LVM2 logical volume for swap".

• "Creating an LVM2 logical volume for swap"
• "Extending swap on an LVM2 logical volume"
• "Creating a swap file (on a filesystem)"

Similar for RHEL-9:

• Extending swap on an LVM2 logical volume
• Creating an LVM2 logical volume for swap
• Creating a swap file

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