Dell SRDF Introduction

Read operations from R2 devices

Reading data from R2 devices directly from a host connected to the R2 is not recommended, because:

• SRDF/S relies on the application’s ability to determine if the data image is the most current. The array at the R2 side may not yet know that data in transmission on the SRDF links has been sent.
• If the remote host reads data from the R2 device while a write I/O is in transit on the SRDF links, the host is not reading the most current data.

Dell Technologies strongly recommends that you allow the remote host to read data from the R2 devices while in Read-Only mode only when:

• Related applications on the production host are stopped.
• The SRDF writes to the R2 devices are blocked due to a temporary suspension/split of the SRDF relationship.

In a mainframe environment, however, PPRC does allow secondary devices to be defined as read-only. Dell Technologies supports this with extra controls in SCF, AutoSwap, and ConGroup software. Such a configuration is known as Host Read Only (HRD).