What type of disk caching should I choose?

On larger plans (starting from HM-3) it is possible for the user to select the disk caching: none, writeback, writeehrough, directsync, unsafe.

When selecting the type of disk caching in KVM virtualization, you must consider the requirements for speed, data security and availability of the storage. 

Let's examine each type of caching:

Writeback - With this type of caching, writes are cached first and then asynchronously written to disk. This increases speed by minimizing the number of writes to disk, but increases the risk of data loss in the event of a power failure or system crash.

Write-through - With this type of caching, data is written immediately to disk and then stored in the cache. This ensures that the data is not lost, but can slow down performance by requiring write operations to disk.

Directsync - with this type of caching all write operations occur synchronously, that is, data is written to disk immediately after it is written to the cache. This ensures data safety, but may decrease performance, because the disk write operations may take extra time.

Unsafe - This type of caching does not use cache, and data is written to disk immediately. This type of caching can be useful if you want to minimize the risk of data loss, but may decrease performance.

Thus, the choice of caching type depends on your speed and data integrity requirements. Writeback provides high performance, but may lead to data loss in case of a sudden server shutdown. Write-through and Directsync guarantee data safety, but may decrease performance. Unsafe can be useful if you need to minimize the risk of data loss, but can reduce performance.