Vous aussi, devenez incollable sur la Haute Dispo d’Exchange ! Session technique, en Anglais, faite par le gourou des technos de haute disponibilité d’Exchange : Scott Schnoll. Scott est speaker aux TechReady et TechEd de Microsoft, a écrit de nombreux livres de référence, et il sera présent en exclusivité pour animer cette session. Parmi les thèmes abordés : Comment séparer mon flux de réplication des logs de mon flux client ? quand un DAG (Database Availability Group) tombe, comment le système choisit-il la bonne copie de la base de données à répliquer ? Allez au-delà des fonctions de base de la haute disponibilité et apprenez ce qui se passe réellement dans les arcanes d’un DAG Exchange. Cette session couvre le fonctionnement interne des DAGs, nous discuterons des réseaux de DAGs, d’Active Manager, de comment le système permet la sélection des meilleures réplications de bases et du Datacenter Activation Coordination Mode.

1. palais des
congrès
Paris
7, 8 et 9
février 2012

2. Exchange Server 2010
High Availability Deep
Dive
08-févr-12
Scott Schnoll
Principal Technical Writer
Microsoft Corporation
MSG306

3. Agenda
Exchange Server 2010 High Availability Deep Dive
 Quorum
 Witness, Witness Server, and Alternate Witness Server
 Database Availability Group Networks
 Active Manager
 Best Copy Selection
 Datacenter Activation Coordination Mode

4. Exchange Server 2010
High Availability
Concept: Quorum

5. Quorum
Used to ensure that only one subset of members is functioning at one
time
Requires a majority of members to be active and have communications
with each other
Represents a shared view of members (voters and some resources)
Dual Usage
 Data shared between the voters representing configuration, etc.
 Number of voters required for the solution to stay running (majority); quorum
is a consensus of voters
 When a majority of voters can communicate with each other, the cluster has
quorum
 When a majority of voters cannot communicate with each other, the cluster does
not have quorum

6. Quorum
Quorum is necessary for cluster functions and for DAG functions
 The DAG must have quorum in order to mount and activate databases
Exchange 2010 uses only two of the four cluster quorum models
 Node Majority (DAGs with an odd number of members)
 Node and File Share Majority (DAGs with an even number of members)
Quorum = (V/2) + 1 (whole numbers only)
 6 members: (6/2) + 1 = 4 votes for quorum (can lose 3 voters)
 9 members: (9/2) + 1 = 5 votes for quorum (can lose 4 voters)
 13 members: (13/2) + 1 = 7 votes for quorum (can lose 6 voters)
 15 members: (15/2) + 1 = 8 votes for quorum (can lose 7 voters)

8. Exchange Server 2010
High Availability
Concept: Witness, Witness Server and Alternate
Witness Server

9. Witness and Witness Server
A witness is a share on a server that is external to the
DAG that participates in quorum by providing a weighted
vote for the DAG member that has a lock on the
witness.log file
 Configured for all DAGs
 Used only by DAGs that have an even number of
members
Witness server does not maintain a copy of quorum data,
does not vote, and is not a member of the DAG or cluster

10. V
XXX

11. XX

12. Alternate Witness Server
Witness server used by a DAG after a datacenter
switchover
DAG is configured to use alternate witness server when
you run Restore-DatabaseAvailabilityGroup or
ahead of time by using Set-
DatabaseAvailabilityGroup
DAGs do not dynamically switch witness servers
 Alternate witness server does not provide redundancy
for witness server or FSW resource

13. Exchange Server 2010
High Availability
Deep Dive: Database Availability Group
Networks

14. DAG Networks
A DAG network is a collection of one or more subnets
There are two types of DAG networks
 MAPI Network - connects DAG members to network resources
(Active Directory, other Exchange servers, DNS, etc.)
 Registered in DNS / DNS configured
 Uses default gateway
 Client for Microsoft Networks/File and Print Sharing enabled
 Replication Network - used for/by continuous replication (log shipping
and seeding)
 Not registered in DNS / DNS not configured
 Typically no default gateway
 Client for Microsoft Networks/File and Print Sharing disabled

15. DAG Networks
Maximum round trip return latency between all DAG
members must be 500 ms or less
 Regardless of the latency of the solution, customers
should validate that the network between all DAG
members is capable of satisfying the data protection
and availability goals of the deployment
 May need to investigate increasing the number of
databases or decreasing the number of mailboxes per
database to achieve desired goals

16. DAG Networks
All DAGs must have:
 Exactly one MAPI network
 Zero or more Replication networks
 Separate network(s) on separate subnet(s)
 LRU determines which replication network is used with
multiple replication networks
DAG networks automatically created when server is added to
DAG
 Based on cluster’s enumeration of networks
 Cluster enumeration based on subnet
 One cluster network is created for each subnet

17. DAG Networks
Server / Network IP Address / Subnet Bits Default Gateway
EX1 – MAPI 192.168.0.15/24 192.168.0.1
EX1 – REPLICATION 10.0.0.15/24 N/A
EX2 – MAPI 192.168.0.16/24 192.168.0.1
EX2 – REPLICATION 10.0.0.16/24 N/A
Name Subnet(s) Interface(s) MAPI Access Enabled Replication Enabled
DAGNetwork01 192.168.0.0/24 EX1 (192.168.0.15) True True
EX2 (192.168.0.16)
DAGNetwork02 10.0.0.0/24 EX1 (10.0.0.15) False True
EX2 (10.0.0.16)

18. DAG Networks
Server / Network IP Address / Subnet Bits Default Gateway
EX1 – MAPI 192.168.0.15/24 192.168.0.1
EX1 – REPLICATION 10.0.0.15/24 N/A
EX2 – MAPI 192.168.1.15/24 192.168.1.1
EX2 – REPLICATION 10.0.1.15/24 N/A
Name Subnet(s) Interface(s) MAPI Access Enabled Replication Enabled
DAGNetwork01 192.168.0.0/24 EX1 (192.168.0.15) True True
DAGNetwork02 10.0.0.0/24 EX1 (10.0.0.15) False True
DAGNetwork03 192.168.1.0/24 EX2 (192.168.1.15) True True
DAGNetwork04 10.0.1.0/24 EX2 (10.0.1.15) False True

19. DAG Networks
Collapse subnets into two DAG networks and disable replication
for the MAPI network:
Set-DatabaseAvailabilityGroupNetwork -Identity DAG2DAGNetwork01 -Subnets
192.168.0.0,192.168.1.0 -ReplicationEnabled:$false
Set-DatabaseAvailabilityGroupNetwork -Identity DAG2DAGNetwork02 -Subnets
10.0.0.0,10.0.1.0
Remove-DatabaseAvailabilityGroupNetwork -Identity DAG2DAGNetwork03
Remove-DatabaseAvailabilityGroupNetwork -Identity DAG2DAGNetwork04
Name Subnet(s) Interface(s) MAPI Access Enabled Replication Enabled
DAGNetwork01 192.168.0.0/24 EX1 (192.168.0.15) True True
DAGNetwork02 10.0.0.0/24 EX1 (10.0.0.15) False True
DAGNetwork03 192.168.1.0/24 EX2 (192.168.1.15) True True
DAGNetwork04 10.0.1.0/24 EX2 (10.0.1.15) False True

20. DAG Networks
Collapse subnets into two DAG networks and disable replication
for the MAPI network:
Set-DatabaseAvailabilityGroupNetwork -Identity DAG2DAGNetwork01 -Subnets
192.168.0.0,192.168.1.0 -ReplicationEnabled:$false
Set-DatabaseAvailabilityGroupNetwork -Identity DAG2DAGNetwork02 -Subnets
10.0.0.0,10.0.1.0
Remove-DatabaseAvailabilityGroupNetwork -Identity DAG2DAGNetwork03
Remove-DatabaseAvailabilityGroupNetwork -Identity DAG2DAGNetwork04
Name Subnet(s) Interface(s) MAPI Access Enabled Replication Enabled
DAGNetwork01 192.168.0.0/24 EX1 (192.168.0.15) True False
192.168.1.0/24 EX2 (192.168.1.15)
DAGNetwork02 10.0.0.0/24 EX1 (10.0.0.15) False True
10.0.1.0/24 EX2 (10.0.1.15)

21. Exchange Server 2010
High Availability
Deep Dive: Active Manager

22. Active Manager
Exchange component that manages high availability
platform
 Runs inside the Microsoft Exchange Replication
service on every Mailbox server
 Is the definitive source of information on where a
database is active
 Stores this information in cluster database
 Provides this information to Active Manager client
running on other server roles (Client Access and
Hub Transport)

23. Active Manager Roles
Standalone Active Manager
Primary Active Manager (PAM)
Standby Active Manager (SAM)
Active Manager Client
 Runs in RPC Client Access service on CAS
and Transport service on Hub

24. Active Manager
Primary Active Manager (PAM)
 Runs on the node that owns the cluster core
resources (cluster group)
 Gets topology change notifications
 Reacts to server failures
 Selects the best database copy on failovers and
targetless switchovers
 Detects failures of local Information Store and local
databases

25. Active Manager
Standby Active Manager (SAM)
 Runs on every other node in the DAG
 Detects failures of local Information Store and local
databases
 Reacts to failures by asking PAM to initiate a failover
 Responds to queries from CAS/Hub about which server
hosts the active copy
Both roles are necessary for automatic recovery
 If the Microsoft Exchange Replication service is stopped,
automatic recovery will not happen

26. Active Manager Functionality
Mount and Dismount Databases
Provide Database Availability Information
Provide Interface for Administrative Tasks
Maintains Database and Server State
Information
Monitor for Failures and Initiate Recovery

27. Exchange Server 2010
High Availability
Deep Dive: Best Copy Selection

28. Best Copy Selection
Process of finding the best copy of an individual
database to activate, given a list potential copies for
activation and their status
Active Manager selects the “best” copy to become
the new active copy when the existing active copy
fails or when an administrator performs a targetless
switchover

29. Best Copy Selection – RTM
Sorts copies by copy queue length to minimize data
loss, using activation preference as a secondary sorting
key if necessary
Selects from sorted listed based on which set of criteria
met by each copy
Attempt Copy Last Logs (ACLL) runs and attempts to copy
missing log files from previous active copy

30. Best Copy Selection – SP1 and
later copies by activation preference when auto database
Sorts
mount dial is set to Lossless
 Otherwise, sorts copies based on copy queue
length, with activation preference used a secondary
sorting key if necessary
Selects from sorted listed based on which set of criteria
met by each copy
Attempt Copy Last Logs (ACLL) runs and attempts to copy
missing log files from previous active copy

31. Best Copy Selection
Is database mountable?
 Is copy queue length <= AutoDatabaseMountDial?
 If Yes, database is marked as current active and
mount request is issued
 If not, next best database tried (if one is available)
During best copy selection, any servers that are
unreachable or “activation blocked” are ignored

32. Best Copy Selection
Criteria Copy Queue Length Replay Queue Length Content Index Status
1 < 10 logs < 50 logs Healthy
2 < 10 logs < 50 logs Crawling
3 N/A < 50 logs Healthy
4 N/A < 50 logs Crawling
5 N/A < 50 logs N/A
6 < 10 logs N/A Healthy
7 < 10 logs N/A Crawling
8 N/A N/A Healthy
9 N/A N/A Crawling
10 Any database copy with a status of Healthy, DisconnectedAndHealthy,
DisconnectedAndResynchronizing, or SeedingSource

33. Best Copy Selection – RTM
Four copies of DB1
DB1 currently active on Server1
Server1 Server2 Server3 Server4
Database Copy Activation Copy Queue
XDB1
Replay Queue
DB1
CI State
DB1 DB1
Database State
Preference Length Length
Server2DB1 2 4 0 Healthy Healthy
Server3DB1 3 2 2 Healthy DiscAndHealthy
Server4DB1 4 10 0 Crawling Healthy

34. Best Copy Selection – RTM
Sort list of available copies based by Copy Queue Length
(using AP as secondary sort key if necessary):
 Server3DB1
 Server2DB1
 Server4DB1
Database Copy Activation Copy Queue Replay Queue CI State Database State
Preference Length Length
Server2DB1 2 4 0 Healthy Healthy
Server3DB1 3 2 2 Healthy DiscAndHealthy
Server4DB1 4 10 0 Crawling Healthy

35. Best Copy Selection – RTM
Only two copies meet first set of criteria for activation
(CQL< 10; RQL< 50; CI=Healthy):
 Server3DB1 Lowest copy queue length – tried first
 Server2DB1
 Server4DB1
Database Copy Activation Copy Queue Replay Queue CI State Database State
Preference Length Length
Server2DB1 2 4 0 Healthy Healthy
Server3DB1 3 2 2 Healthy DiscAndHealthy
Server4DB1 4 10 0 Crawling Healthy

36. Best Copy Selection – SP1 and
later copies of DB1
Four
DB1 currently active on Server1
Auto database mount
Server1 Server2 Server3 Server4
dial set to Lossless
Database Copy Activation Copy Queue
XDB1
Replay Queue
DB1
CI State
DB1 DB1
Database State
Preference Length Length
Server2DB1 2 4 0 Healthy Healthy
Server3DB1 3 2 2 Healthy DiscAndHealthy
Server4DB1 4 10 0 Crawling Healthy

37. Best Copy Selection – SP1 and
later list of available copies based by Activation
Sort
Preference:
 Server2DB1
 Server3DB1
 Server4DB1
Database Copy Activation Copy Queue Replay Queue CI State Database State
Preference Length Length
Server2DB1 2 4 0 Healthy Healthy
Server3DB1 3 2 2 Healthy DiscAndHealthy
Server4DB1 4 10 0 Crawling Healthy

38. Best Copy Selection – SP1 and
later list of available copies based by Activation
Sort
Preference: Lowest preference value – tried first
 Server2DB1
 Server3DB1
 Server4DB1
Database Copy Activation Copy Queue Replay Queue CI State Database State
Preference Length Length
Server2DB1 2 4 0 Healthy Healthy
Server3DB1 3 2 2 Healthy DiscAndHealthy
Server4DB1 4 10 0 Crawling Healthy

39. Best Copy Selection
After Active Manager determines the best copy to activate
 The Replication service on the target server attempts
to copy missing log files from the source (ACLL)
 If successful, then the database will mount with
zero data loss
 If unsuccessful (lossy failure), then the database
will mount based on the AutoDatabaseMountDial
setting
 If data loss is outside of dial setting, next copy will
be tried

40. Best Copy Selection
After Active Manager determines the best copy to activate
 The mounted database will generate new log files
(using the same log generation sequence)
 Transport Dumpster requests will be initiated for the
mounted database to recover lost messages
 When original server or database recovers, it will run
through divergence detection and either perform an
incremental resync or require a full reseed

41. Exchange Server 2010
High Availability
Deep Dive: Datacenter Activation Coordination
Mode

42. DAC Mode
Datacenter Activation Coordination (DAC) mode is a property
setting of a DAG
Acts as an application-level form of quorum
 Designed to prevent multiple copies of same database
mounting on different members due to loss of network
Also enables use of Site Resilience cmdlets
 Stop-DatabaseAvailabilityGroup
 Restore-DatabaseAvailabilityGroup
 Start-DatabaseAvailabilityGroup

43. DAC Mode
Exchange 2010 RTM
 DAC Mode is only for DAGs with three or more
members that are extended to two Active Directory
sites
Exchange 2010 SP1 and later
 DAC Mode can (and should) be enabled for all DAGs

44. DAC Mode
Uses Datacenter Activation Coordination Protocol (DACP),
which is a bit in memory set to either:
 0 = can’t mount
 1 = can mount

45. DAC Mode
Active Manager startup sequence
 DACP is set to 0
 DAG member communicates with other DAG members it
can reach to determine the current value for their DACP bits
 If the starting DAG member can communicate with all
other members, DACP bit switches to 1
 If other DACP bits are set to 0, starting DAG member
DACP bit remains at 0
 If another DACP bit is set to 1, starting DAG member
DACP bit switches to 1

46. DAC Mode
Secondary Datacenter
Primary Datacenter
Outlook Outlook
DAG1 HT2010 CAS-Pri CAS-Sec HT2010
FSW
DAG1 Active Active
MBX-A MBX-B MBX-C MBX-D

47. DAC Mode
Secondary Datacenter
Primary Datacenter
Outlook Outlook
AWS
DAG1 HT2010 CAS-Pri CAS-Sec HT2010
FSW
DAG1 Active Active
MBX-A MBX-B MBX-C MBX-D

48. DAC Mode
Secondary Datacenter
Primary Datacenter
Outlook Outlook
AWS
DAG1 HT2010 CAS-Pri CAS-Sec HT2010
FSW
DAG1 Active Active
0 0 1 1
MBX-A MBX-B MBX-C MBX-D

49. Questions?
Thank you for attending!
Contact me at any time with questions:
 scott.schnoll@microsoft.com
 Twitter: @schnoll
 Blog: http://blogs.technet.com/scottschnoll

50. © 2012 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and
Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.