SRDF Device States

While performing SRDF operations, SRDF devices (Check my blog for details on various SRDF Devices) may undergo various kind of transitional states like any standard device and SRDF device transitions that are unique to SRDF devices. You can determine the state of the devices after examining the R1 and R2 devices and their mirror states. Enginuity 5874 onwards, you can check the time stamp when this state transition has happened and the cause behind this.

SRDF device states can be determined by a combination of 2 views :

1. Host interface view - Reflects the SRDF device state as seen by the host
2. SRDF view - Reflects the SRDF mirror states and internal device state

Host Interface View :
Host interface view reflects the SRDF device states as seen by the hosts which are connected to the device

R1 Device States: R1 device can have any one of the below states

• Read/Write                                - In this state host will be able to perform read and write operations on the device. This is default R1 device state.

• Read Only (Write Disabled)      - In this state host will only be able to read from the device but write operations will be disabled for the device.

• Not Ready                                 - In this state R1 device responds Not Ready to the host for any read and write operations.

Also check Dominos Mode and Data Integrity.

R2 Device States: R2 device can have any one of the below states

• Read Only (Write Disabled)      - In this state host will only be able to read from the device but write operations will be disabled for the device.

• Read/Write                                - In this state host will be able to perform read and write operations on the device. We can see this state during recovery or parallel processing from R1 and R2

• Not Ready                                 - In this state R2 device responds Not Ready to the host for any read and write operations.

Invalid tracks Attributes:

If used with special device attributes,the invalid tracks attributes, the not ready state of the R2 device provides information about the state of SRDF device pair i.e. whether they are usable for business operation or not. Invalid Track attributes can only be set on R2 devices. This attribute tells you that there are invalid tracks which are still not synchronized to R2 devices. If the invalid track attribute is set on R2 devices, Enginuity will make the R2 device Not Ready to the host if the secondary device is not synchronized with R1 device.

In case of a disaster, invalid track attribute helps you in deciding whether to use the R2 devices for recovery or not. If the devices becomes Not Ready due to invalid track attributes, data might not be suitable for business operations. There is option of resetting the Not Ready attribute by using host based software.

SRDF View :
SRDF view reflects the SRDF mirror states and internal device state and also tells whether the device is ready for SRDF operation or not.

R1 Device States: R1 device can have any one of the below states for SRDF operations.

• Ready     - This condition occurs when the R1 device is able to send the data across SRDF links. It will remain valid even if the local mirror fails or are not ready for the I/O operations as it will not have any impact on the SRDF operations.

• Not Ready (SRDF mirror Not Ready) - This condition occurs when R1 device is not Not Ready for SRDF operations. It is important to understand that this is an R1 SRDF mirror state and not R1 or R2 device state. This condition occurs when the remote mirroring is halted and updates are not been pushed to R2 device. Invalid tracks keeps accounting on R1 SRDF mirror. When the R2 device's host interface view is Read/Write enabled, R1 will automatically be in "Not Ready" SRDF view state.

R2 Device States: R2 device can have any one of the below states for SRDF operations.

• Ready    - R2 device is able to receive the updates from R1 device and device is also able to get host based software commands.

• Not Ready-This state is actually confusing, confuses me every time if I just see the name. In this state actually R2 device can receive updates from R1 device but only restriction will be that it can not receive host based software commands.

• Link Blocked (lnkBlk)- This state is specific to R2 SRDF mirrors and belong to SRDF R22 devices (Check my blog for details on various SRDF Devices). In this state one of the R2 SRDF mirror can not receive the data from it's associated R1 device.