Dell SRDF Introduction

Permanent link loss (SRDF/A)

If all SRDF links are lost for more time than link limbo or Transmit Idle can manage:

• All of the devices in the SRDF group are set to a Not Ready state.
• All data in capture and transmit delta sets is changed from write pending for the R1 SRDF mirror to invalid for the R1 SRDF mirror and is therefore owed to the R2 device.
• Any new write I/Os to the R1 device are also marked invalid for the R1 SRDF mirror.

  These tracks are owed to the secondary array once the links are restored.

When the links are restored, normal SRDF recovery procedures are followed:

• Metadata representing the data owed is compared and merged based on normal host recovery procedures.
• Data is resynchronized by sending the owed tracks as part of the SRDF/A cycles.

Data on non-consistency exempt devices on the secondary array is always dependent-write consistent in SRDF/A active/consistent state, even when all SRDF links fail. Starting a resynchronization process compromises the dependent-write consistency until the resynchronization is fully complete and two cycle switches have occurred.

For this reason, it is important to use TimeFinder to create a gold copy of the dependent-write consistent image on the secondary array.