ubuntu 20.10 should include dm-vdo support

[Rafael David Tinoco]

Ubuntu should also include support for dm-vdo technology:

"
VDO (which includes kvdo and vdo) is software that provides inline block-level deduplication, compression, and thin provisioning capabilities for primary storage. VDO installs within the Linux device mapper framework, where it takes ownership of existing physical block devices and remaps these to new, higher-level block devices with data-efficiency capabilities.

Deduplication is a technique for reducing the consumption of storage resources by eliminating multiple copies of duplicate blocks. Compression takes the individual unique blocks and shrinks them with coding algorithms; these reduced blocks are then efficiently packed together into physical blocks. Thin provisioning manages the mapping from LBAs presented by VDO to where the data has actually been stored, and also eliminates any blocks of all zeroes.

With deduplication, instead of writing the same data more than once each duplicate block is detected and recorded as a reference to the original block. VDO maintains a mapping from logical block addresses (used by the storage layer above VDO) to physical block addresses (used by the storage layer under VDO). After deduplication, multiple logical block addresses may be mapped to the same physical block address; these are called shared blocks and are reference-counted by the software.

With VDO's compression, multiple blocks (or shared blocks) are compressed with the fast LZ4 algorithm, and binned together where possible so that multiple compressed blocks fit within a 4 KB block on the underlying storage. Mapping from LBA is to a physical block address and index within it for the desired compressed data. All compressed blocks are individually reference counted for correctness.

Block sharing and block compression are invisible to applications using the storage, which read and write blocks as they would if VDO were not present. When a shared block is overwritten, a new physical block is allocated for storing the new block data to ensure that other logical block addresses that are mapped to the shared physical block are not modified.

This public source release of VDO includes two kernel modules, and a set of userspace tools for managing them. The "kvdo" module implements fine-grained storage virtualization, thin provisioning, block sharing, and compression; the "uds" module provides memory-efficient duplicate identification. The userspace tools include a pair of python scripts, "vdo" for creating and managing VDO volumes, and "vdostats" for extracting statistics from those volumes.
"

https://github.com/dm-vdo

https://github.com/dm-vdo/vdo

[Joshua West (jwest66346)]

5.11.0-22-generic can no longer compile kvdo from source, failing with:

```
Skipping BTF generation for /src/kvdo/vdo/kvdo.ko due to unavailability of vmlinux
make: Leaving directory '/usr/src/linux-headers-5.11.0-22-generic'
```

Even though ddebs + dbgsym are installed. :(

An Ubuntu package / support for dm-vdo would be hugely impactful.