As covered in Chapter 2, Database Hardware, how fast data can actually be committed permanently to disk is a critical performance aspect for database transaction processing. It's important to measure this area carefully. Speeds that are dramatically higher than expected are usually a sign that one of the write-caches has been put into a volatile write-back mode, which, as already explained, can result in data loss and database corruption. Some examples of how that can happen will be covered in Chapter 4, Disk Setup.
If you don't have any non-volatile caching available, the basic commit rate for a drive will be similar to its IOPS rating. Luckily, PostgreSQL will put multiple transactions into a physical commit if they aren't happening ...
