Why it happens - logging to DCM (needs dcm resynchronization)

[Zahid_Haseeb]

Replicated Data Set: RVG

Primary:

  Host name:                  X.X.X.X

  RVG name:                   RVG

  DG name:                    DG

  RVG state:                  enabled for I/O

  Data volumes:               1

  VSets:                      0

  SRL name:                   SRL

  SRL size:                   100.00 G

  Total secondaries:          1

Secondary:

  Host name:                  X.X.X.X

  RVG name:                   RVG

  DG name:                    DG

  Data status:                consistent, behind

  Replication status:         logging to DCM (needs dcm resynchronization)

  Current mode:               asynchronous

  Logging to:                 DCM (contains 89718720 Kbytes) (SRL protection logging)

  Timestamp Information:      N/A

I know the problem will be resolved via running the below command. But why it happen ? cant this be automated ?

vxrvg -g dg resync rvg

(Client dont have any disconnection between Primary and DR site)

[Gaurav_S · Accepted solution]

Hi Zahid,

DCM is a additional level of protection given for your SRL flow ... You can imagine it as level 2  while level 1 is SRL itself .

Till the data is filling in SRL, its automatically replicated to DR site however once SRL overflows, then DCM protection kicks on & the starts tracking the blocks where data has changed.

In such situations VVR can't on its own decide to push data because there is no write order fidelity maintained. Hence you need to trigger command manually which will just map all the changed blocks to DR site & bringing DR site back in sync

G

[Marianne · Accepted solution]

Gaurav has pointed out the real issue here:

... once SRL overflows, then DCM protection kicks on ...

If this happens on a regular basis, you need to find out why:
Are there more network outages than the SRL can handle?
Insufficient bandwidth?
Increased I/O on source server?
Was SRL simply created too small?