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Chapter 1. Introduction to VDO on LVM
The Virtual Data Optimizer (VDO) feature provides inline block-level deduplication, compression, and thin provisioning for storage. You can manage VDO as a type of LVM logical volumes (LVs), similar to LVM thinly provisioned volumes.
VDO volumes on LVM (LVM-VDO) are composed of the following LVs:
- VDO pool LV
This is the backing physical device that stores, deduplicates, and compresses data for the VDO LV. The VDO pool LV sets the physical size of the VDO volume, which is the amount of data that VDO can store on the disk.
Currently, each VDO pool LV can hold only one VDO LV. As a result, VDO deduplicated and compresses each VDO LV separately. In other words, VDO cannot deduplicate or compress a piece of data that is shared between several VDO LV.
- VDO LV
- This is the virtual, provisioned device on top of the VDO pool LV. The VDO LV sets the provisioned, logical size of the VDO volume, which is the amount of data that applications can write to the volume before deduplication and compression occurs.
Table 1.1. A comparison of components in VDO on LVM and LVM thin provisioning
| Physical device | Provisioned device | |
|---|---|---|
| VDO on LVM | VDO pool LV | VDO LV |
| LVM thin provisioning | Thin pool | Thin volume |
Since VDO is thinly provisioned, the file system and applications only see the logical space in use and are not aware of the actual physical space available. Use scripting to monitor the actual available space and generate an alert if use exceeds a threshold: for example, when the VDO pool LV is 80% full.