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 GAD two quorum disk configuration situation

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Matija Šinogl's profile image
Matija Šinogl posted 04-03-2019 15:01

Hi, i am planning to implement GAD in a 2DC enviroment. it is recommended to configure quorum disk on the primary site. i am planning to configure quorum in primary and secondary DC.

this way i will have quorum redundancy, but does anyone have any idea what will happen if primary site losses connection to the secondary site?

in theory, both quorum disk will be alive, one will see P-VOL and will consider it as secondary site failure and operations will continue as planned, but how will quorum and S-VOL on secondary site act

is such a scenario even possible?

In a 3DC scenario, if both P-VOL and S-VOL loose connection to quorum, P-VOL operations (R/W) should continue?

John Mcdevitt's profile image
John Mcdevitt

Matija --

Your GAD configuration cannot have more than one quorum device for a given set of pairs.  In a 2DC configuration, please configure the quorum device in the primary site.  If the quorum array were to fail, GAD will stay active/active as long as there are no other failures (status checks are made using the replication links to keep GAD A/A).  You could then do a quorum replacement if needed, or just fix the quorum array.

Regardless of if quorum is hosted in the same site as the Pvol or in a 3rd site, if both P-Vol and S-Vol array can communicate with each other, we will maintain Active/Active GAD operations.  Quorum device is there to mediate the "winner" when the P-Vol and S-Vol array cannot talk to each other.  We want the quorum in the primary site in a 2DC configuration so that the primary site will continue if there is a network outage between the two sites.

Matija Šinogl's profile image
Matija Šinogl

Ok, thank you for the clarification.

In a 2DC scenario where quorum is on a primary site, when primary site fails (storage and quorum), secondary site, S-VOLs will be blocked. Is there any possibility that we can use S-VOLs from secondary site?

Maybe some manual procedure?

Can we replicate quorum disk (true copy) to the secondary site and in a case of the primary site failure, recover it on the second site and bring S-VOL in Read-write state?

Any suggestion for this scenario would be welcome

John Mcdevitt's profile image
John Mcdevitt

If the primary site fails such that the GAD array in the secondary site loses access to both the primary array and the quorum at the same time, the SVols will be blocked (because the secondary array cannot know if it is the only healthy array, or if it is just network isolated from the other two arrays).  You can recover access to the S-Vols by forcibly deleting the pairs.  The process for this is discussed in the GAD manual.