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MaxMedov
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Sep 12, 2023

Number of DCDs

Hello, I saw in a few F5 docs that installing three DCDs instead of one or two is more recommended.
I understood the benefit of two DCDs due to the redundancy of replicas, but why is it recommended to have three? 
We need to understand how much resources to relocate for that project and have to decide the number of DCDs.
Are there any other benefits except the redundancy? (We have two DCs, so that will be two or three in each zone.)
Is three better during the restoration process? Upgrade?
I cannot find a direct answer to that.

Thank you for your answer!

  • If you have 3 DCD then the shard mirroring between the DCD will be like 30%. How to explain imagine that DCD 1 goes down then to restore the missing statistics data DCD 2 and DCD 3 will use their own information, so when you have 3 DCD it is not like each one having the exact same copy of the other 2 and it is more opimized.

     

    It is like RAID 1 when you have 2 DCD and RAID 5 when you have 3 DCD:

    https://en.wikipedia.org/wiki/RAID

3 Replies

  • If you have 3 DCD then the shard mirroring between the DCD will be like 30%. How to explain imagine that DCD 1 goes down then to restore the missing statistics data DCD 2 and DCD 3 will use their own information, so when you have 3 DCD it is not like each one having the exact same copy of the other 2 and it is more opimized.

     

    It is like RAID 1 when you have 2 DCD and RAID 5 when you have 3 DCD:

    https://en.wikipedia.org/wiki/RAID