A: On each disk a policy can be configured to enable or disable write caching (see screen shot below).

writecache-sml
writecache-sml

Write caching enables the OS to tell an application or process that a write to disk has been performed, allowing processing to continue, while in reality the device caches the write-in memory to write out at a later time as part of other writes to optimize performance.

This means potentially if there were a power outage, the write would never occur, and data loss or corruption could occur. Connecting the computer to an Uninterruptible Power Supply (UPS) offers some protection from power failure, making the use of write caching less risky, but power failure isn't the only problem to consider. Other failures could also occur:

  • Physical hardware failure/crash
  • OS crash

In either of the above scenarios, a UPS doesn't offer protection from possible data loss or corruption caused by write caching. I should stress that data loss or corruption is only "possible" and by no means a certainty.

The reality is that the writes often take place very quickly. Still you need to consider this. To answer the question, although write caching does improve performance, its benefit should be carefully balanced against the cost of possible data loss or corruption, and a UPS should always be present if write caching is enabled.