RHCSA RHEL 8 – Configure disk compression

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This video is based on RHEL 8. Video to cover the section ‘Configure disk compression’ for the RHCSA (Red Hat Certified System Administrator).

More information on the required learning: http://bit.ly/rhcsa8

Notes from the video:

With Virtual Data Optimizer (VDO) it is possible to trade CPU/RAM resources for disk space.  This allows compression of files without the requirement of using gzip, rar or other compression tools.

Regarding use cases, VDO can, for example, be used under local filesystems, iSCSI or Ceph.

To install the application:

# yum install vdo kmod-kvdo

If you have an existing LVM from the previous videos you’ll need to unmount and remove:

# umount /mnt

Remove the fstab entry and run fdisk to delete the partitions created earlier.

# fdisk /dev/sdb

Use the d option to delete the partitions and w to write the changes.

Create the VDO volume:

# vdo create --name=vdo1 --device=/dev/sdb \ --vdoLogicalSize=30G --writePolicy=auto

VDO supports three write modes:

• The ‘sync’ mode, where writes to the VDO device are acknowledged when the underlying storage has written the data permanently.
• The ‘async’ mode, where writes are acknowledged before being written to persistent storage. In this mode, VDO is also obeying flush requests from the layers above. So even in async mode it can safely deal with your data – equivalent to other devices with volatile write back caches. This is the right mode, if your storage itself is reporting writes as ‘done’ when they are not guaranteed to be written.
• The ‘auto’ mode, now the default, which selects async or sync write policy based on the capabilities of the underlying storage.

Then create the underlying filesystem:

# mkfs.xfs /dev/mapper/vdo1

Mount the new disk:

# mount /dev/mapper/vdo1 /mnt