Product : Microsoft, HyperV/2019, DataCenter
Feature : Caching, Storage, Network and Storage
Content Owner:  Roman Macek
Summary
CSV Cache; Write-Back Cache - Storage Spaces Direct Cache
Details
In WS 2012 R2 there are two main features to provide perfromance improvements through caching

1. CSV Cache:
Windows Server 2012 introduced the CSV cache to provide (READ) caching on the block level by allocating system memory (RAM) as cache. This can significantly improve Hyper-V read performance (e.g. VDI boot storms).

New in WS 20012 R2:
- In Windows Server 2012, you could allocate only 20% of the total physical RAM to the CSV cache. You can now allocate up to 80%.
- In Windows Server 2012, the CSV cache was disabled by default. In Windows Server 2012 R2, it is enabled by default.

2. Storage Spaces Write- Back Caching:
Storage Spaces can use existing SSDs in the storage pool to create a write-back cache that buffers small random writes to SSDs before later writing them to HDDs.
- write-back cache is transparent to administrators and users and is created on all new virtual disks as long as there is a sufficient number of SSDs in the storage pool (Simple spaces: one SSD, Two-way mirror spaces and single-parity spaces: two SSDs, three-way mirror spaces and dual parity spaces: three SSDs)
- write-back cache works with all types of storage spaces, including storage spaces with storage tiers
- newly created storage spaces automatically use a 1 GB write-back cache (as long as the storage pool contains enough disks with MediaType set to SSD or Usage set to Journal)

3 - The Storage Spaces Direct provides a highly available cache system based on the fastest storage devices. In production it is recommended to deploy two storage devices. Storage Spaces Direct requires Windows Server 2016 Datacenter edition.