红帽全球峰会第 3 章 Creating a deduplicated and compressed logical volume
You can create an LVM logical volume that uses the VDO feature to deduplicate and compress data.
3.1. The physical and logical size of an LVM-VDO volume
VDO calculates physical, available physical, and logical sizes for LVM-VDO volumes, emphasizing size relationships, storage efficiency, provisioning best practices, and capacity limits.
VDO uses different definitions of size:
- Physical size
This is the same size as the physical extents allocated to the VDO pool LV. VDO uses this storage for:
- User data, which might be deduplicated and compressed
- VDO metadata, such as the UDS index
- Available physical size
This is the portion of the physical size that VDO is able to use for user data.
It is equivalent to the physical size minus the size of the metadata, rounded down to a multiple of the slab size.
- Logical Size
This is the provisioned size that the VDO LV presents to applications. It is usually larger than the available physical size. VDO currently supports any logical size up to 254 times the size of the physical volume with an absolute maximum logical size of 4 PB.
When you set up a VDO logical volume (LV), you specify the amount of logical storage that the VDO LV presents. When hosting active virtual machines (VMs) or containers, use provisioning storage at a 10:1 logical to physical ratio. For example, if you are utilizing 1 TB of physical storage, you would present it as 10 TB of logical storage.
If you do not specify the
--virtualsizeoption, VDO provisions the volume to a1:1ratio. For example, if you put a VDO LV on top of a 20 GB VDO pool LV, VDO reserves 2.5 GB for the UDS index, if the default index size is used. The remaining 17.5 GB is provided for the VDO metadata and user data. As a result, the available storage to consume is not more than 17.5 GB, and can be less due to metadata that makes up the actual VDO volume.
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