What is Microsoft Exchange Server?
Exchange Server is an enterprise-class collaboration tool that primarily focuses upon sending, receiving, and storing email messages. Exchange Server offers many collaboration features such as calendaring and tight integration with Microsoft Office applications.
Microsoft Exchange Server is Microsoft’s email, calendaring and contact platform. It is also used for collaboration and scheduling purposes. It’s deployed on Windows Server OS for business use. Microsoft created Exchange Server to allow users to access the messaging platform via mobile devices, desktops, and web-based systems. Voice messages are supported by Exchange Server’s telephony capabilities.
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Users of Exchange collaborate via calendar and document sharing. The platform’s storage and security features allow organizations to archive content, perform searches, and complete compliance tasks. Exchange Server evolved over time and is now a core component of Office 365, a Microsoft cloud-based software-as-a service (SaaS) from Microsoft Corp.
MS Exchange Server is well-known for its high availability (HA), which ensures that service continues in all outage situations. This includes designing paths that can provide service even during server failures and data center outages.
Exchange Server 2019 Features
The 2019 version provides faster and more reliable failover among servers. It is designed to increase overall performance and take advantage the most recent storage hardware, such as larger disks or solid-state drives (SSDs).
Exchange server 2019 also includes the following features:
- Supports up to 48 CPU cores and 256GB memory.
- Allows for Windows Server Core installations.
- External access to Exchange admin Center (EAC), and the Exchange Management Shell can be blocked natively.
- Dynamic memory cache allocation is used to optimize memory usage for active database.
- This prevents attendees receiving invitations to meetings.
- Provides end users additional Out of Office options.
- Administrators can cancel meetings that were arranged by users who have left the company.
- Administrators have the ability to assign delegate rights.
- Allows email addresses with non-English characters to route and be delivered natively.
- There is a new logo for Exchange Server 2019.
- These additional features were removed from Exchange 2019 along with the Unified Messaging role and all associated functionality.
The Exchange Team website posted a Sept. 16, 2019, blog indicating that Microsoft would extend support for Exchange Server 2010 from Jan. 14 to Oct. 13 2020 to allow Exchange Server 2010 customers more time for their migrations. The January 14, 2020 end of life for Exchange Server 201 0 means Administrators using Exchange Server 2010 projects/tasks on Windows Server 2008 will need to make adjustments.
Exchange Server 2019 Requirements
To install Exchange 2019, you must meet the following requirements:
- Exchange 2019 can only be installed in Active Directory forests that already contain Exchange 2016 or 2013 servers. Exchange 2019 cannot be installed in an existing forest that contains Exchange 2016 or 2013.
- All domain controllers (DCs), in an AD forest, must run Windows Server 2019 Standard, Datacenter or Windows Server 2016 Standard, or Windows Server 2012 R2 Standard, or Datacenter.
- The AD forest function level should be Windows Server 2012R2 or higher.
- Exchange 2019 hosting server must have a 64-bit processor.
- Server hosting Exchange 2019 should contain between 128 and 2256 gigabytes of random access memory.
- New Technology File System (NTFS), is required for all disk partitions containing Exchange binaries, diagnostic logs, transport database, and system partition. Resilient File System may be used for partitions that contain transaction logs and mailbox databases.
Exchange Server High Availability
Exchange Server provides several key features that help to ensure resilience and HA. Mailbox server components of Exchange depend on database availability groups (DAGs). Load balancing is a requirement for components of the client access server.
Database Availability Groups
The Database Availability Group (DAG) is the core Exchange subsystem that ensures HA. DAG was introduced in Exchange 2010. It quickly rose to prominence and became one of the most essential subsystems within Exchange.
A DAG is a group consisting of up to 16 Exchange servers which automatically copies databases among members to provide redundancy in case of failure at the server or database level. A DAG member server can host a copy from another member server. A copy of a database can be added to any server. This copy is kept up-to-date and is available for activation at any time.
The DAG is not based on technology specific to the Exchange Team, but Windows Clustering. This could mean that Windows Server features and bugs can sometimes have a significant effect on Exchange’s functionality.
Active Manager (AM) is an Exchange component responsible for managing failover events in an Exchange environment. AM is available in Microsoft Exchange Replication Service for all Exchange 2016 servers. Two AM roles are available when an Exchange server is connected to a DAG: Standby Active Manager (SAM) and Primary Active Manager (PAM).
The PAM role will be held by the DAG member server which owns the cluster-quorum resource. The DAG member server that holds the cluster quorum resource will lose the PAM role.
The SAM provides information to other Exchange components running AM clients regarding which database copy is active. The SAM is responsible for detecting a failed database and asking the PAM to start the failover event. The SAM does not have the responsibility of deciding which database copy is activated after a failure. This process is known as best copy and server selection (BCSS).
Exchange Server’s Best Copy Selection
AM steps in to repair a database problem by choosing the best copy of the database to activate. The BCSS process is described as follows:
- Failures are detected by AM and Managed Availability. Administrators can initiate a non targeted switching process.
- The PAM initiates the internal BCSS algorithm.
- The sub-process attempt copy last logs attempts to copy any log files that are not present on the server hosting the active copy.
- When the ACLL process completes, an AutoDatabaseMountDial value is checked for servers hosting copies of the database and is compared to the copy queue length of the database being activated. If the number of missing log files is less than or equal to the value of AutoDatabaseMountDial, AM moves on to step five. AM will continue the process at step two if it is not.
- The PAM issues an information store mount request. AM returns to step 2 if the database fails to mount.
If a monitoring event triggers the failover event, there is additional logic. This logic will ensure that the server that takes over the active database is in a better state than the one it came from.
The Database Availability Group (DAG) Quorum Modes
A DAG refers to a specific implementation for a Windows Server Cluster. DAGs’ Exchange components rely on the technology of Windows Server Cluster to function. To understand how to implement and manage DAGs, it is important to know the concept of quorum.
Quorum refers to the idea that in the event of the death of one or more DAG members there are rules to determine what resources can be provided by the remaining members. These quorum rules sets are used to ensure consistent operation of DAGs and act as a tiebreaker when DAG nodes cease communication.
If a DAG contains an even number nodes, it uses Node & File Majority Quorum mode. An external witness server acts in this mode as the tiebreaker. In this mode, each DAG member receives one vote. However, the witness server gives an additional vote to one of the DAG members. Each member has their own local disk containing the cluster quorum data. However, the witness server has an additional file that points to the DAG member with the most recent copy of the DAG cluster data.
Node Majority Quorum
Node Majority Quorum mode is used when a DAG has an odd number members. This mode gives each DAG member a vote and stores cluster quorum data on each member’s local disk.
You can manually assign DAG members with weighted votes to specific DAG members. This is not recommended and should be discussed with Microsoft support.
Exchange Server Datacenter Activation Coordination (DAC) Mode
Datacenter Activation Coordination mode is a DAG feature that prevents two databases from being live on different servers due to an outage. DAC mode is only available when the server hosting the database can’t reach a majority (or more) of the DAG member servers.
Microsoft best practices recommend that DAC mode be enabled on all DAGs with two or more members and which use continuous replication. DAC mode is only recommended for DAGs that have more than two members and use continuous replication.
When DAC is active there is additional communication among DAG nodes at startup using the DAC Protocol (DACP). DACP is set at 0 upon startup. AM will not attempt any database creation on the node if the DACP bit is set to 0. If another DAG member has their DACP bits set to 1, or when a DAG Node can contact all servers in its DAG membership, the DACP bit may be set to 1.
DAC mode can be used when a primary or backup data center fails. DAC mode stops different databases from being active in the two data centers when power is restored and servers are up.
DAC mode compares the boot time of two DAG members and the time that the DACP bit was first set to 1 in order to determine if the DAG can mount databases. If the DACP bit was set earlier than the boot times of the alternate witness servers, it assumes that both servers were restarted simultaneously. This could be due to a power outage at the primary data center. The DAG member cannot mount databases. The system will assume that it is safe to mount database if the DACP bit has been set to 1 after the boot of the alternate witness servers.
Database Availability Group Split-Brain Conditions And Cmdlets
Split brain refers to two databases that are active simultaneously in different data centers. This can lead to the possibility of losing user data if the two databases become divergent.
In addition to preventing split-brain conditions, DAC mode enables Database Availability Group cmdlets to be started, stopped and restored. These cmdlets can be used to perform manual data center switchovers. If DAC mode is disabled, manual data center switching is difficult and requires both Exchange tools as well as a cluster manager.
Imagine an Exchange environment consisting of four servers each with a copy the same database.
Two servers from this environment are located in data center A, and two in data center B. The link between the data centers is affected by a network failure. Without DAC mode disabled, servers in each data center would think they need to activate a backup of the database.
DAC mode prevents split-brain scenarios by requiring that nodes must have majority before a database can activate. Node majority is the requirement that all nodes within the cluster, or DAG in this instance, must be available and reachable in order for a DAG to activate a copy of a database. To determine the node majority, the file share witness can also vote.
With a four-node cluster, two nodes per data center and two nodes each, the Exchange servers with the file share witness in the data centers would only be able activate databases in the above example. The DAG nodes located in the other data center would not be able to activate any databases until they could contact all DAG members.
Exchange Server Third-Site Witness
Exchange 2013 added support for third-site witnesses. This feature allows users to bring all their resources online, without the need to be contacted by administrators. Each site will have its own network path to the third site witness so that nodes at each site can maintain quorum by using the witness server. Exchange administrators must take the time to understand the network behavior of third-site witnesses.
Load Balancing With Exchange Server
Administrators can use load balancing to control which network traffic is directed to each Exchange server in a network. It is common to manage the distributions of incoming client connections between Exchange 2016 servers:
- To spread the work load. It’s a smart idea to have multiple Exchange servers work regularly if someone has to set up and maintain multiple Exchange servers.
- To minimize the consequences of a failure. It’s helpful to have an alternative system that can take over for the system that has failed.
Load balancing is an addition to DAGs. DAGs are responsible for (1) ensuring that each mailbox has multiple copies and (2) accepting client requests in the event that an active copy is unavailable. Load balancing is similar. Its job is to ensure that client traffic can be sent to other locations in the event that one becomes unavailable.
Load balancing may be performed on one site or multiple sites. It can involve two or more Exchange servers. A Preferred Architecture (PA), Exchange deployment would have four Exchange servers spread across two AD sites. Exchange supports Layer 4, Layer 7, and round-robin load balancing for domain names (DNS).
Exchange Server Preferred Architecture (PA)
The ideal Exchange deployment is Exchange Preferred Architecture (PA), according to the Exchange Team at Microsoft. The PA was designed with total cost-of-ownership (TCO), Hight Availability (HA) and resiliency as well as redundancy, redundancy, and recovery in mind. The PA was not created to be used to model maturity. It was intended to inspire.
The Exchange Server Clients
Users of Exchange can access and interact with messages via an email client. Microsoft Outlook is the most popular client. Exchange Server 2016 supports the following:
- Outlook 2016
- Outlook 2013
- Outlook 2010 Service Pack 2 SP2
- Outlook for Mac for Office 365 Outlook for Mac 2011
Outlook can also be accessed via the web as Outlook on the Web (formerly Outlook Web App, commonly abbreviated OWA). This allows users to interact with and access messages from different web browsers. Outlook on the Web allows users to link and share documents stored on OneDrive for Business on an on-premises SharePoint Server. This makes it easier for users to attach files to emails and save them in a more direct manner.
Exchange Server Pros And Cons
Although it’s easy to discuss the benefits of Microsoft Exchange, it can be hard to find any cons. There are very few, if any, true rivals to Exchange at the moment.
Exchange Online and Exchange on-premises have the most active users, but Microsoft doesn’t release any numbers. Outlook.com runs on Exchange. Exchange Online, Exchange Online, and Exchange on-premises all have more users than Gmail (business/personal). Other messaging platforms, other than Microsoft’s and Googles, have smaller business user bases.
Lotus Notes is the most popular business messaging platform after Google and Microsoft. Because Notes is not a messaging platform, it’s difficult to compare Exchange and Notes. Lotus Notes is a database solution with messaging functionality. HCL has purchased ownership of Lotus Notes from IBM. This means that the product will no longer be updated.
Zimbra is the most popular Linux-based messaging platform. Both on-premises and Serial Attached Serial-Attached SAS (SAS), Zimbra solutions are available. Open source Zimbra versions are also available. They offer different licensing options.
It is difficult to compare the pros and cons of different messaging solutions, each with its own features and focuses. Here are some top-level pro/con comparisons. These lists are not meant to be exhaustive.
Exchange Server On-Premises Vs. Exchange Server Online
For businesses searching for a messaging solution, the most popular choice will be Exchange on-premises or Exchange Online.
- Administrators have the ability to control feature availability and upgrade schedule.
- Administrators are responsible for hardware repairs.
- One-time licensing fee.
- Administrators are responsible for hardware repairs.
- Must be kept on-site, locally.
- Access to servers and data must not be granted to anyone outside of the company.
Exchange Server Online vs. Gmail Exchange Server Online
- Integrates with other Office 365 program applications.
- Integration hybrid-style with Exchange Server on-premises
- Integration with Office 365 applications is more expensive than Gmail
Pros And Cons Of Gmail
- Gmail is less expensive than Exchange Server Online
- No options for Hybrid
- Fewer software features than Exchange Server Online suite of software
- No Administrator Integration
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