The Even Read feature distributes data reads evenly across all the disks in a disk group. For each I/O request presented to the system, there may be one or more disks that contain the data. With this feature, each request to read can be sent to the least loaded of the possible source disks.
The Even Read functionality is enabled by default on all Oracle Database and Oracle ASM instances of version 12.1 and higher in non-Exadata environments. The functionality is enabled in an Exadata environment when there is a failure.