Host caching works by bringing storage closer to the VM that can be written or read to quickly. The amount of storage that is available to the VM for host caching is in the documentation.
A virtual machine’s cached limits are separate from its uncached limits. This means you can enable host caching on disks attached to a VM while not enabling host caching on other disks.
This configuration allows your virtual machines to get a total storage IO of the cached limit plus the uncached limit.
https://learn.microsoft.com/en-us/azure/virtual-machines/disks-performance
Ephemeral OS disks are created on the local virtual machine (VM) storage and not saved to the remote Azure Storage.
Ephemeral OS disk can be stored either on VM’s OS cache disk or VM’s temp/resource disk.
https://learn.microsoft.com/en-us/azure/virtual-machines/ephemeral-os-disks
Caching uses specialized (and sometimes expensive) temporary storage that has faster read and write performance than permanent storage. Because cache storage is often limited, you need to make decisions as to what data operations will benefit most from caching. But even where the cache can be made widely available, such as in Azure, it’s still important to know the workload patterns of each disk before deciding which caching type to use.
https://learn.microsoft.com/en-us/training/modules/caching-and-performance-azure-storage-and-disks/3-enable-and-configure-azure-vm-disk-cache-by-using-the-azure-portal
Caching in Azure storage is a feature that is used to improve disk performance and reduce latency while accessing the data. Azure premium storage uses Blobcache technology to create a pool of RAM and SSD storage to save cache data. Caching stores data that is being accessed the first time, in a combination of RAM and local SSDs for future uses. When you access that data next time it will not be accessed from a storage device rather it will be accessed directly from the cache. The write operation will first be done in cache data and then replicated this change to the storage system.
We can use the disk caching feature on OS and Data disks to increase their performance.
Disk caching for any Azure storage disks is configured or managed by choosing the appropriate option for Host Caching setting for disk storage.
We can use any disk caching option (Read, Read\write, None) for OS and data disks whereas temporary disk does not use any type of disk caching.
https://www.sqlshack.com/importance-of-disk-caching-in-azure-storage-disks-for-sql-server-workloads/
Daniel Velasco (notes?) 