Powersafe Overwrite

Powersafe Overwrite

"Powersafe overwrite" is a term used by the SQLite team to describe a behavior of some filesystems and disk-controllers related to data preservation during a power loss. Powersafe overwrite is a boolean property: either the storage system has it or it does not.

We say that a system has the powersafe overwrite property if the following statement is true:

 When an application writes a range of bytes in a file, no bytes outside of that range will change, even if the write occurs just before a crash or power failure. 

The powersafe overwrite property says nothing about the state of the bytes that were written. Those bytes might contain their old values, their new values, random values, or some combination of these. The powersafe overwrite property merely states that writes cannot change bytes outside of the range of bytes written.

In other words, powersafe overwrite means that there is no