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New Member

Synchronous Storage Replication Process


I have a question regarding storage replication for synchronous mode. If I describe the process in detail having twin Data Centers called DC-A and DC-B we have:

1- The server in DC-A writes to the DC-A disk.

2-  Before the server in DC-A receives an ACK from the DC-A disk, this data is replicated to the other DC disk, DC-B Disk.

3-  To replicate the data to the other DC we will first ask to the other DC before passing through the DCI “are you ready to receive”?

4-  We will get the approval from DC-B that is ready

5-  Then DC-A will send the data through the DCI to arrive to DC-B.

6-  DC-B disk receives de data and then DC-B disk must send an ACK to DC-A Disk

7-  Once the ACK is received at DC-A disk, DC-A disk will then send the ACK to the server in DC-A which originated the write action.

My question is if step 3 and 4 sometimes are counted and sometimes not. I should counted or not? This decision is important for me because it affects by a factor of 2 the distance between the twin DCs.

Thank you very much for the help.



Everyone's tags (3)
New Member

Synchronous Storage Replication Process


just to add more information. My doubt comes from the 2 Cisco live sessions about DCI.

On this session it says that we must count 4 times the traffic passing through the DCI in order to know the DCI Distance:

On this other session it says that we must count only 2 times:

Who is right then? because the impact is huge.

Thank you.




Synchronous Storage Replication Process

The whole discussion around round trip delay refers to the clasical fibre channel protocol

p 13 refers to a classical FC write operation, which requires 2 round trip

p 15 is a optimization: Cisco Write Acceleration feature on MDS Fabric; the local switch proxies the first RT, by sending a OK to the initiator; therefore, only one round trip