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Page 1 of 30Uncovering Exchange 2010 Database Availability Groups (DA...

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High Availability & Recovery

Uncovering Exchange 2010 Database

Availability Groups (DAGs) (Part 4)

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Download a free trial!What Exchange 2010 Database Availability Groups is all about

and how they may fit into your enterprise. I will also provide

you with step by step instructions on how you deploy DAG in a

lab environment.

Published:Apr 08, 2010

Updated:Dec 15, 2010 Section:High Availability & Recovery Author:Henrik Walther Printable Version

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Figure 1: Suspending a Database copy

To do the same via the EMS, you can use the following command:

Suspend-MailboxDatabaseCopy Identity MDB02\E14EX02

In order to resume a database copy using the EMC, you just right-click on it again

and choose Resume Database Copy.




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Figure 2: Resuming a Database Copy

If you rather want to resume it using the EMS, run the following command:

Resume-MailboxDatabaseCopy Identity MDB02\E14EX02

Moving the Active Database Copy to another DAG

Member (aka Switchover)

When you have a planned outage and need to take a DAG member that holds one ormore active database copies down for maintenance, its considered best practice to

manually move any active database copies (aka performing a switchover) to another

DAG member in the DAG. To move an active database copy to another DAGmember using the EMC is accomplished by right-clicking on the respective

database(s) and selecting Move Active Mailbox Database in the context menu as

shown in Figure 3.




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Figure 3: Activating a Database Copy

This brings up the Activate a Database Copy wizard (Figure 4).

Figure 4: Activate Database Copy wizard

Here we can see the name of the database and on which DAG member it currently is

mounted. To move the database copy to another DAG member, clickBrowse.




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Figure 5: Selecting the server holding the database copy to be activated

When you have selected the DAG member on which the databse copy should beactivated, clickOK. Then decide if you want to change the database mount dial

settings on the target mailbox server. As you can see in Figure 6 its set to None(change nothing) by default. If you want to change the current setting (set to Best

Availability by default) instead choose Lossless, Best Effort, or Best Availability.

Figure 6: Automatic database mount dial settings

Heres a description of each of the available database mount dial settings:

Lossless: (when selecting Lossless the database will not mount automatically

until all logs generated on the active database copy has been copied to the

passive database copy) Good Availability: (when selecting Good Availability, the database will mount

automatically as long as you have a copy queue length less than or equal to 6. Ifthe copy queue holds more than 6 log files, the database will not mount)

Best Effort: (with Best Effort the database will mount no matter the copyqueue length. Be careful with this setting as you could loose a lot of mailbox

data!)

Best Availability: (with Best Availbility the database will mount automatically

as long as the copy queue length is less than or equal to 12. If the copy queuelength is more than 12, the database will not be able to mount)




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Unless theres a specific reason to chose another database mount dial override than

the setting currently configured, leave this option at None. When you are ready to

activate the database copy in the target mailbox server specified, clickMove.

To activiate a database copy using the EMS, we can use the following command:

Move-ActiveMailboxDatabase MDB01 -ActivateOnServer E14EX02 -

MountDialOverride:None

Seeding Database Copies

There may be times where you need to seed a database copy for one reason or theother. This can both be done via the Exchange Management Console (EMC) and the

Exchange Management Shell (EMS). Let us take a look at how to accomplish thisvia the EMC.

If it is not already the case, the first thing we must do is to suspend replication for

the passive database copy we want to seed.




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Figure 7: Suspending the Database Copy

You will now be presented with a dialog box where you can enter a comment on

why replication for the database copy is being suspended.

Figure 8: Dialog box for optional comment

When suspended, right-click on the database copy once again and select UpdateDatabase Copy.




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Figure 9: Selecting update Database copy in the context menu

The Update Database Copy wizard will now appear (Figure 10).

Figure 10: Update database copy wizard

As you can see we have several options in this wizard. We have the option ofspecifying the source server that should be used for seeding. This is a really cool

feature since you are no longer limited to seeding from an active database copy as

was the case in with Exchange 2007 LCR/CCR/SCR.

Page 10 of 30Uncovering Exchange 2010 Database Availability Groups (D...



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Figure 11: Selecting source seeding server

We can also choose the behavior when files exist in the target path. In addition, wecan specify whether replication to this database copy should be resumes or whether

it should be leaved suspended.

Lastly, we can select which DAG network should be used to seed the database copy.

Again a great feature, which although it was an option in Exchange 2007 SP1, was

very cumbersome.

Figure 12: Selecting DAG network used for seeding database copy

When you have chosen your settings, click Update in order to seed the database

copy. When the seeding has completed, clickFinish.




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Figure 13: Seeding process completed successfully

If you rather want to use the EMS to seed a database copy, the above could be

accomplished by first suspending replication with:

Suspend-MailboxDatabaseCopy Identity MDB02\E14EX02

Figure 14: Suspending a database copy via the Exchange Management Shell

Then run the following command to re-seed the database copy:

Update-MailboxDatabaseCopy -Identity MDB02\E14EX02




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Figure 15: Seeding a database copy via the Exchange Management Shell

Changing the Log file Replication Port

In Exchange 2007, the Microsoft Exchange Replication Service copies log files to

the passive database copy (LCR), passive cluster node (CCR) or SCR target over

Server Message Block (SMB). With DAGs in Exchange 2010, the asynchronousreplication technology no longer relies on SMB. Instead, Exchange 2010 uses

TCP/IP for log file copying and seeding and, even better; it provides the option of

specifying which port you want to use for log file replication. By default, DAG usesTCP port 64327, but you are free to specify whatever port you want to use. To seethe current port used, you must use the Get-AvailabilityGroup cmdlet with the

Status parameter. To see the port used in our lab environment, use:

Get-DatabaseAvailabilityGroup DAG1 Status | fl

Figure 16: Checking Replication port settings for a DAG

To change the port used we must use Exchange Management Shell (EMS) as thisoption isnt included in the Exchange Management Console (EMC). Since this




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setting is configured per DAG, we must use the Set-DatabaseAvailabilityGroupcmdlet.

For instance to change the port for the DAG in our lab to TCP port 7580, we mustuse the following command:

Set-DatabaseAvailabilityGroup DAG1 -ReplicationPort 7580

When the port have been changed, we can verify the new setting using:

Get-DatabaseAvailabilityGroup DAG1 Status | fl ReplicationPort

Figure 17: Checking new Replication port settings for a DAG

Now when updating a database copy, we can see that TCP/7580 is used (below I ran

Netstat an while the database copy were updated.

Figure 18: Checking the new replication port is used (by running Netstat -an)




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Log file Network Compression

With DAGs in Exchange 2010, we can enable or disable compression for seedingand replication activities over one or more networks in a DAG. This is a property of

the DAG itself, not a DAG network. The default setting isInterSubnetOnly (which

means compression is used when replication occur across subnets) as shown inFigure 19.

Figure 19: Checking Network Compression settings for a DAG

The available values are:

Disabled (disabled on all networks)

Enabled (enabled on all networks)

InterSubnetOnly (enabled for inter-subnet communication only) SeedOnly (enabled only for seeding)

If we for instance want to enable network compression for log file copying and

seeding on all networks in a DAG in our lab environment, we would use thefollowing command:

Set-DatabaseAvailabilityGroup DAG1 -NetworkCompression Enabled




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Figure 20: Checking new Network Compression settings for a DAG

With compression enabled for log file seeding and replication, you can expectaround 30% compression ratio. As you can see, theres really no reason why you

should disable network compression unless you for instance use a 3rd party

WAN/network optimizer that doesnt support DAG network compression.

Log file Network Encryption

With DAGs in Exchange 2010 theres now native support for encryption of log file

seeding and replication activities. In Exchange 2007 log files are copied over an

unencrypted channel unless IPsec has been configured. DAG leverages theencryption capabilities of Windows Server 2008/R2, that is DAG uses Kerberos

authentication between each DAG member. Network encryption is a property of the

DAG itself, not the DAG network. Available settings for the network encryption

property are:

Disabled (network encryption not in use),

Enabled (network encryption enabled for seeding and replication on all

networks associated with a DAG), InterSubnetOnly (the default setting meaning network encryption is used

across subnets)

SeedOnly (network encryption in use for seeding on all networks in a DAG).

The default setting is InterSubnetOnly.




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Figure 21: Checking Network Encryption settings for a DAG

If you want to change the network encryption settings, you can use the Set-DatabaseAvailabilityGroupcmdlet. For instance, if you wanted to enable encryption

for log copying and seeding on all networks, you would use the following

command:

Set-DatabaseAvailabilityGroup -identity DAG1 -NetworkEncryption Enabled

Figure 22: Checking new Network Encryptions settings for a DAG

Configuring Replay & Truncation Lag Time

The Standby Continuous Replication (SCR) feature that was introduced with

Exchange 2007 SP1 gave us the option of replicating one or more databases from astand-alone mailbox server, cluster continuous replication (CCR) cluster, or single

copy cluster (SCC) to a target stand-alone mailbox server or standby cluster (CCR

or SCC failover cluster where only the passive clustered mailbox role has beeninstalled). SCR could both be used for replicating storage groups locally in a

datacenter or remotely to servers located in a secondary or backup datacenter.




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In addition to being able to replicate data to multiple targets per storage group, SCRalso introduced the concept of replay lag time and truncation lag time. With replay

lag time you could configure the Microsoft Exchange Replication service to wait for

a specified amount of time before log files that had been copied from the SCR

source to the SCR target(s) were replayed. The default value for replay lag time was

24 hours and could be configured with a value of up to 7 days (if configured to 0seconds there were a 50 log files lag time so that a reseed wasnt require when a

lossy failover has occurred). The idea with replay lag time was to have a database

from back in time, which could be used to recover if active database copy/copies onthe SCR source server(s) were struck by logical corruption. This way to can stop

replication before the logical corruption is replicated to the SCR target server(s) and

thereby prevent loosing data.

Truncation lag time could be used to specify how long the Microsoft Exchange

Replication service should wait before truncating (deleting) the log files that had

been copied to the SCR target server (s) and replayed into the copy of the database(s). The maximum allowable setting for truncation lag time is 7 days and the

minimum is 0 seconds, which will remove the truncation delay completely. With

truncation lag time you could recover from failures that affected the log files on the

SCR source server(s).

DAG also supports replay lag time and truncation lag time we know from SCR in

Exchange 2007 SP1. They work pretty much the same way although controlled via

a new cmdlet (Set-MailboxDatabaseCopy).

These features have been improved a little with Exchange 2010. For instance, the

replay lag time option now has a maximum setting of 14 days instead of 7 days as

was the case with Exchange 2007 SP1. Also bear in mind that unlike SCR inExchange 2007 SP1, replay lag time in Exchange 2010 does not have a hard-coded

replay lag of 50 log files (even when set to 0 seconds).

As you can see in Figure 23 both replay and truncation lag time are disabled by

default.




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Figure 23: Default Replay and Truncation Lag time setting for a Mailbox database

The purpose with replay and truncation lag time in Exchange 2010 is pretty much

the same as with SCR in Exchange 2007 SP1 that is to protect against database

logical corruption and store logical corruption. Whats interesting and new with

Exchange 2010 is you now can use lagged database copies in combination withlegal hold etc.

I wont dive further into lagged database copies in this multi-part article. Instead Illcover this topic in a future articles here on MSExchange.org.

Blocking a Database Copy from being activated




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adver t isement

There are situations where you might want to block a passive database copy (or

even server) in a DAG from being changed activated (changed to the active

database copy). Good thing is the Exchange Product group thought about this kindof scenario. You can do exactly that using a so called activation policy. Its not

possible to use the EMC to set this, but using the EMS, you can use the Suspend-

MailboxDatabaseCopy cmdlet for this purpose. Yes correct, this cmdlet is typically

used for suspending replication for a database copy, but when run with a specialActivationOnly parameter, you can block a database copy from being changed to

the active database copy during a failover. For instance, if we want to block MDB01

on E14EX02 from ever being activated during a failover, we can use the following

command:

Suspend-MailboxDatabaseCopy Identity MDB01\E14EX02 -ActivationOnly

Figure 24: Blocking a database copy from being activated

Notice this does not suspend replication for the database copy and thereby result in,an over time, huge copy queue. Only the database copy is being block from

activation.




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Figure 25: Replication not suspended when using Suspend-MailboxDatabaseCopywith the ActivationOnly parameter

When this cmdlet is run with theActivationOnly parameter, the database copy

cannot be activated until the following command is run:

Resume-MailboxDatabaseCopy Identity MDB01\E14EX02

Figure 26: Unblocking a database copy from being activated

Ok so what if I wish to block all databases on a DAG member server? Will I then

need to run the above command on all database copies on the particular server?Luckily not. We have a similar command that works on the server level. If oyu want

to block a DAG member instead use the Set-MailboxServer with the

DatabaseCopyAutoActivationPolicy Blockedparameter.

For instance if I wanted to block DAG member E14EX02 from having databasecopies activated, I would use the following command:

Set-MailboxServer Identity E14EX02 - DatabaseCopyAutoActivationPolicy

Blocked

Figure 27: Blocking a DAG member from being activated

To allow database copies to be activated again, I would replace Blocked withUnrestricted:

Set-MailboxServer Identity E14EX02 - DatabaseCopyAutoActivationPolicy

Unrestricted




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Tariq Samsudeen Works at Fortune Promoseven

Very clear. Amazing piece of info.

Reply Like 4 March at 18:51




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Henrik Walther is a respected writer with special focus on Microsoft

Exchange and Office 365/BPOS (Exchange Online) solutions within the unified

communications area. Prior to joining Microsoft, he was an eight year Exchange

MVP and back in 2006 he took the Microsoft Certified Master: Exchangecertification.

Click here for Henrik Walther's section.

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