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DRL, DCO, fastsync recommendations for Campus Cluster on Windows

Level 6
Partner Accredited

 I have a couple of questions regarding using DRL, DCO and fastsync in SFW.  I am using 6.0, but answers are probably applicable to all versions:

  1. What are the recommendations for using DRL and DCO in a 2 site campus cluster?
    In solution guide for SFW for 6.0 and latest 7.3, there is a "Campus Cluster" section, within which is a "Creating/Planning diskgroups and volumes", but DRLs and DCOs are not mentioned.  My thoughts are (per volume):
    - One DRL should be created (2 are not neccessary unless using JBODs) as if both mirrors are not available then DRL cannot resync mirrors so it doesn't matter which site you put DRL on
    - 2 DCOs should be created, one on each site so that it doesn't matter which array is lost, the other array can keep track of writes
    - The only reason not to create DRLs and DCOs are if you need to push the performance to the extreme where the overhead of writting to DRL/DCO may be significant.

    Note in Linux/UNIX, DRL functionality is built-in to DCO (except in really old version), so only need a DCO, but I believe Windows does not have this feature in any versions.

  2. In Linux/UNIX, having DCOs and setting Fastresync are 2 separate things, so you can have one without the other, so you need to make sure you do both, but on Windows it appears these on one in the same - i.e if you add a DCO, fastsync is on and if you remove all DCOs, then fastsync is off, and if you set fastresync on/off, then a DCO is added/removed and so there is no specific fastresync attribute on the volume that you set independently of DCOs.  So to tell if fastsync is on I think you just need to check there is a DCO on volume - can someone confirm?


Level 6
Partner    VIP    Accredited Certified

Hi @mikebounds

Good to see you around.

The sad thing is that these forums are so quiet lately that no-one seems to even attempt a reply... Smiley Sad

My 2c :

I agree - only one DRL is needed.

I also agree with DCO statements - only used with FMR and DGSJ. 
2 DCO's are needed to keep track of changes on both mirrors during the split.

This old TN for SFW should still be applicable: