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What is the Get-MailboxServerRedundancy cmdlet all about?

Exchange Server 2016Exchange Server 2019

Exchange Server 2016 introduced the PowerShell cmdlet Get-MailboxServerRedundancy. This cmdlet helps you plan and prepare for Exchange Server maintenance by querying the current maintenance readiness of the database availability group (DAG). 

Interestingly, there is no PowerShell help available for this vital cmdlet. Microsoft Docs or Exchange Management Shell's Get-Help provide any valuable information.

When querying a DAG about the server redundancy status, the cmdlet's default output provides you with the essential information.

The default output contains information about:

  • Identity
    Name of the DAG member server
     
  • IsServerFoundInAD
    Indicates if the corresponding server computer object exists Active Directory
     
  • IsInMaintenance
    Indicates if the server is currently in maintenance mode
     
  • RepairUrgency
    Indicates an aggregated state of the mailbox database and search index repair modes 
     
  • SafeForMaintenance
    Indicates if you can safely activate the maintenance mode for this server
     
  • HealthInfoLastUpdateTime
    Timestamp when the server's health state was last updated
     

 

Example - Prior Maintenance

This example shows the Get-MailboxServerRedundancy output of a six server DAG, before activating maintenance mode for server LOCEXS06.

Get-MailboxServerRedundancy -DatabaseAvailabilityGroup EXDAG01

Identity        IsServerFound IsInMainten RepairUrgency SafeForMaintenance HealthInfoLastUpdateTime
                InAD          ance
--------        ------------- ----------- ------------- ------------------ ------------------------
LOCEXS01        True          False       Prohibited    False              17.02.2020 09:10:11
LOCEXS02        True          False       Normal        True               17.02.2020 09:10:11
LOCEXS03        True          False       Normal        True               17.02.2020 09:10:11
LOCEXS06        True          False       Normal        True               17.02.2020 09:10:11
LOCEXS05        True          False       Normal        True               17.02.2020 09:10:11
LOCEXS04        True          False       Prohibited    False              17.02.2020 09:10:11

 

As Exchange Administrator, you are most interested in the information displayed in columns RepairUrgency and SafeForMaintenance.

Screenshot Get-MailboxServerRedundancy

 

As you can see in this screenshot, no server is in maintenance mode. Servers S01 and S04 have a RepairUrgency state of Prohibited, and a SafeForMaintenance state of False. The latter tells us that we cannot activate maintenance mode for servers safely without risking mailbox database redundancy. 

What is the reason for this? Let's have a look.

 

Server Information

You can use the same cmdlet to query detailed information for each member server of the DAG. The default output for a single server does not provide any additional information on the server status. 

Get-MailboxServerRedundancy -DatabaseAvailabilityGroup EXDAG01 -Identity LOCEXS01

Identity        IsServerFound IsInMainten RepairUrgency SafeForMaintenance HealthInfoLastUpdateTime
                InAD          ance
--------        ------------- ----------- ------------- ------------------ ------------------------
LOCEXS01        True          False       Prohibited    False              17.02.2020 09:11:11

 

Because we cannot activate maintenance mode for server LOCEXS01 safely, we are interested in identifying which redundancy state is responsible.

You can find this information by displaying the detailed server information.

 

Detailed Server Information

Use the Format-List, or short FL, cmdlet to display the Get-MailboxServerRedundancy cmdlet output as a formatted list.

Get-MailboxServerRedundancy -DatabaseAvailabilityGroup EXDAG01 -Identity LOCEXS01 | FL

RunspaceId                                  : 70d82f8d-e6ca-4bfc-863f-11300a9784ff
Identity                                    : LOCEXS01
IsServerFoundInAD                           : True
IsInMaintenance                             : False
RepairUrgency                               : Prohibited
SafeForMaintenance                          : False
ServerContactedFqdn                         : LOCEXS04.VARUNAGROUP.DE
HealthInfoCreateTime                        : 15.06.2018 15:16:19
HealthInfoLastUpdateTime                    : 17.02.2020 09:11:11
ServerFoundInAD                             : CurrentState: Active; LastActiveTransition: 15.06.2018 15:22:16;
                                              LastInactiveTransition:
InMaintenance                               : CurrentState: Inactive; LastActiveTransition: 17.01.2020 09:07:02;
                                              LastInactiveTransition: 17.01.2020 10:42:02
AutoActivationPolicyBlocked                 : CurrentState: Inactive; LastActiveTransition: 09.01.2020 10:14:50;
                                              LastInactiveTransition: 09.01.2020 11:00:51
ActivationDisabledAndMoveNow                : CurrentState: Inactive; LastActiveTransition: ; LastInactiveTransition:
                                              15.06.2018 15:22:16
HighAvailabilityComponentStateOffline       : CurrentState: Inactive; LastActiveTransition: 17.01.2020 09:07:02;
                                              LastInactiveTransition: 17.01.2020 10:42:02
CriticalForMaintainingAvailability          : CurrentState: Inactive; LastActiveTransition: 31.01.2020 16:52:49;
                                              LastInactiveTransition: 31.01.2020 16:56:49
CriticalForMaintainingRedundancy            : CurrentState: Active; LastActiveTransition: 29.01.2020 11:43:06;
                                              LastInactiveTransition: 29.01.2020 11:42:06
PotentiallyCriticalForMaintainingRedundancy : CurrentState: Active; LastActiveTransition: 01.02.2020 05:49:37;
                                              LastInactiveTransition:
CriticalForRestoringAvailability            : CurrentState: Inactive; LastActiveTransition: 06.05.2019 09:16:36;
                                              LastInactiveTransition: 06.05.2019 09:20:36
CriticalForRestoringRedundancy              : CurrentState: Inactive; LastActiveTransition: 29.01.2020 11:42:06;
                                              LastInactiveTransition: 29.01.2020 11:43:06
HighForRestoringAvailability                : CurrentState: Inactive; LastActiveTransition: 29.01.2020 11:42:06;
                                              LastInactiveTransition: 29.01.2020 11:43:06
HighForRestoringRedundancy                  : CurrentState: Inactive; LastActiveTransition: 10.02.2020 09:05:02;
                                              LastInactiveTransition: 10.02.2020 09:06:02
IsSafeForMaintenance                        : CurrentState: Inactive; LastActiveTransition: 03.11.2019 09:42:35;
                                              LastInactiveTransition: 12.11.2019 06:29:58
IsValid                                     : True
ObjectState                                 : Unchanged

 

The lines 24-27 show the information we want to know. Both, the CriticalForMaintainingRedundancy and PotentiallyCriticalForMaintainingRedundancy parameters have a CurrentState value of Active. The Primary Activation Manager (PAM) considers the server availability critical to provide redundant availability of the database copies hosted by this server. 

Each of state-parameter shows three pieces of information:

  • CurrentState
    The current state, either Active  or Inactive
     
  • LastActiveTransition
    The timestamp of the last state change to Active
     
  • LastInactiveTransition
    The timestamp of the last state change to Inactive

 

I cover the different state-parameters in a future blog post. 


But there is still the bothering question of why are two of the six servers not safe for activating maintenance?

The reason is simple. The mailbox databases mounted by the member servers of the DAG have a different number of database copies. This configuration is due to data storage capacity constraints.

The mailbox databases storing primary user mailboxes use four database copies per database. Those copies are evenly distributed across all six mailbox servers. Mailbox database storing online archive mailboxes use three copies per database. This database copy layout allows for safely activating server maintenance for one server at a time without risk to database redundancy.

The servers LOCEXS01 and LOCEXS04 hold mailbox databases with just two copies per configured database. Placing one of those two servers into maintenance mode reduces the database availability for these mailbox databases to one. Therefore, PAM informs us that database redundancy is at risk when activating maintenance for those two servers. 

 

Example - During Maintenance

This example shows the member server redundancy state while LOCEXS06 is in maintenance. The reason for monthly maintenance for installing Windows updates.

Maintenance was activated using the StartDagServerMaintenance.ps1 PowerShell script.

 

Get-MailboxServerRedundancy -DatabaseAvailabilityGroup indag01

Identity        IsServerFound IsInMainten RepairUrgency SafeForMaintenance HealthInfoLastUpdateTime
                InAD          ance
--------        ------------- ----------- ------------- ------------------ ------------------------
LOCEXS01        True          False       Prohibited    False              17.02.2020 11:04:12
LOCEXS02        True          False       Normal        True               17.02.2020 11:04:12
LOCEXS03        True          False       Prohibited    False              17.02.2020 11:04:12
LOCEXS06        True          True        High          True               17.02.2020 11:04:12
LOCEXS05        True          False       Prohibited    False              17.02.2020 11:04:12
LOCEXS04        True          False       Prohibited    False              17.02.2020 11:04:12

Having a single server in maintenance has a significant impact on all other servers in the DAG. The servers LOCEXS03 and LOCEXS05 are not safe for maintenance as well. Activating maintenance for those two servers would affect the database redundancy for the databases hosted by those two servers.

 

Example - After Maintenance

After completing all maintenance tasks, e.g., installing Windows Updates or a new Exchange Server Cumulative Update, you end server maintenance using the PowerShell script StopDagServerMaintenance.ps1.

We query the server redundancy state again. 

Get-MailboxServerRedundancy -DatabaseAvailabilityGroup indag01

Identity        IsServerFound IsInMainten RepairUrgency SafeForMaintenance HealthInfoLastUpdateTime
                InAD          ance
--------        ------------- ----------- ------------- ------------------ ------------------------
LOCEXS01        True          False       Prohibited    False              17.02.2020 11:23:12
LOCEXS02        True          False       Normal        True               17.02.2020 11:23:12
LOCEXS03        True          False       Normal        True               17.02.2020 11:23:12
LOCEXS06        True          False       High          True               17.02.2020 11:23:12
LOCEXS05        True          False       Normal        True               17.02.2020 11:23:12
LOCEXS04        True          False       Prohibited    False              17.02.2020 11:23:12

 

Server LOCEXS06 is not in maintenance, but the RepairUrgency state is High. The local Exchange Server replication engine is still busy replicating and processing log files, and updating the search indices. When CopyQueueLength and ReplayQueueLength are back to 0, and ContentIndexStates are back to Healthy, the RepairUrgency switches to Normal.

 

Tip

  • You receive an error message when activating maintenance for an Exchange Server not safe for maintenance using
    StartDagServerMaintenance.ps1 -serverName [SERVER]

    In this case, you must use:

.\StartDagServerMaintenance.ps1 -serverName SERVERNAME -overrideMinimumTwoCopies:$true

 

Enjoy Exchange Server!

 

 



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