SymptomsDisk performance has become slower after migration onto ext4 filesystem.
CauseThis may happen due to the set of the filesystem features [not] enabled during the mount time. The below features are commonly known to influence the extX filesystem performance:
feature enables/disables the use of write barriers in the journalling block device code. When turned off, it allows you to bypass strict order while writing journal commits.
This feature disables registering a file access time.
This feature allows metadata to be written asynchronously from the corresponding data.
The last feature is enabled by default in ext4 and might be the reason for the visible performance degradation compared to the same device formatted with ext3.
Full information on ext4 features can be accessed from here.