
312 4.9 Fundamentals of storage performance
and provides several orders of magnitude of improved response time, in the
best cases.
Figure 4.57 gives the logical steps involved in performing a write opera-
tion, and compares the sequence of events between cached write operations
and non-cached (a.k.a write-through) operations.
4.9.3 Write-back cache
As explained previously, the write-back decouples the I/O completion from
the actual physical operation. This is beneficial in the case of Exchange
2000, especially for the transaction log files. The caveat is that in a certain
sense, the controller lies to the application and operating system by con-
firming a ...