The set block size must synchronize and purge the disk to avoid an
inconsistent cache state and data corruption. The synchronization is
optional depending on the new sync parameter. In some contexts a
synchronization must not be performed, e.g. during disk creation.
Read-ahead requests were previously executed in the context of the
reading task. This blocks the reading task until the complete read
with read-ahead transfer is finished. A read-ahead task is introduced
to off-load the read-ahead transfer. This allows the reading task to
work with the requested block more quickly. The read-ahead is triggered
after two misses of ascending consecutive blocks or a read hit of a
block read by the most-recent read-ahead transfer. The read-ahead
feature is configurable and can be disabled.
