Mailbox Databases Flashcards
What is the maximum Mailbox Database size?
16 TB
However, this is not recommended, it is merely the theoretical maximum that it can support.
A smaller size is recommended to avoid issues with backup, restore, repair, recovery, and performance.
What is the recommended maximum mailbox database size?
200 GB for non-replicated databases
2 TB for replicated databases.
What is JBOD?
Just a Bunch of Disks
An arrangement of a single physical disk, or multiple disks which are not using RAID, and have no physical redundancy or parity.
When using JBOD, you need to use application-level replication for redundancy,
What is DAG?
Database Availability Group
The mechanism of high availability for Exchange 2016.
When does Microsoft recommend using JBOD?
Microsoft recommends JBOD for Exchange deployments that use DAG, for the database and log volumes (but not the OS volume).
When is NTFS vs. ReFS recommended?
Use NTFS for the OS volume, and the Exchange application volume (which is typically the same volume). ReFS is not compatible.
Volumes storing databases and transaction log files may use either NTFS or ReFS, but ReFS is recommended because of the benefits.
What are the benefits of ReFS?
It’s more resilient.
- Enhanced data verification and auto-correction
- more resilient to file system corruption.
- This is particularly true with volumes hosting large files. (and Exchange DB files are usually large.)
How should ReFS be configured for Exchange?
You should disable integrity streams on Exchange DB and Log volumes, for performance reasons.
This does not disable the benefits of ReFS, and it avoids a serious performance hit.
The GUI can format as ReFS, but does NOT HAVE an option to disable integrity streams, so you must use PowerShell.
Provide an example PowerShell command for formatting a newly added disk meant to store an Exchange database.
(Answer has line breaks inserted for readability.)
Get-Disk 5 | Initialize-Disk -PartitionStyle GPT -PassThru | New-Partition -UseMaximumSize | Format-Volume -FileSystem REFS -NewFileSystemLabel Volume1 -SetIntegrityStreams $false
What is Auto Reseed?
A feature of Exchange 2016 DAGs that automatically detects and recovers from storage failure scenarios.
When a disk fails in a DAG and the Auto Reseed process is triggered, what happens?
Auto Reseed will bring the DAG into a fully healthy state by:
- automatically mounting a disk from a pool of spares (that were preconfigured),
- formatting that disk for use,
- and reseeding the database copies onto the new disk.
What are the storage layout requirements for Auto Reseed?
• JBOD, not RAID
• Multiple databases per volume.
– Number of DBs should equal number of copies of each DB. (4 member DAG should have 4 DBs per volume.)
• Mount points, not drive letters
What will trigger Auto Reseed?
- MSExchange Replication Service checks for database copies that are FailedAndSuspended
- If all database copies on a volume are FailedAndSuspended for 15 minutes, then the Auto Reseed recovery workflow is started.
What configurations are recommended when virtualizing an Exchange server?
- Max of 2:1 ratio of vCPU to logical CPU (1:1 preferred)
- Size the server using MS’s sizing calculator, which adds overhead for virtualization
- Fixed memory allocation (no Dynamic Memory)
- Full storage allocation (no Thin Provisioning)
What common virtualization features are not supported with Exchange?
- Any “hot” migration or failover mechanism that doesn’t start the VM on a new host as a cold boot, except for Hyper-V Live Migration
- Any replication-based disaster recovery solution (MS recommends using DAGs for replication)
- Any use of VM snapshots to “roll back” an Exchange VM to a previous state.
What is Jetstress?
A Microsoft tool that simulates Exchange 2013 and Exchange 2016 disk I/O load on a server to verify the performance and stability of your disk subsystem before putting your server into a production environment.
Jetstress validates that the storage you configure meets the requirements Exchange will have.
When should Jetstress be run?
- On a server before installing Exchange.
- If using RAID volumes, test when volume is both healthy and degraded (because there’s no point to RAID if the volume becomes unusable when degraded)
- If using shared infrastructure (e.g. virtualization), test during peak load times
How does Jetstress work?
Simulates disk I/O load for a given number of users that you specify
and in doing so, it tests:
- Disk hardware
- Storage firmware
- Storage controllers
- File system
How large can a DAG be?
A DAG can consist of up to 16 mailbox servers, plus a FSW server.
What is a FSW?
File Share Witness
Every DAG has one FSW.
A non-DAG member of the DAG, running Windows Server.
It serves as a tie-breaker during quorum voting for DAGs with an even number of members.
How many databases can an Exchange 2016 Standard edition server host?
A maximum of 5 databases
How many databases can an Exchange 2016 Enterprise edition server host?
A maximum of 100 databases
What are the OS and software versioning requirements for DAG members?
DAG Members must:
- All run the same version of Windows Server
- All run the same major version of Exchange:
○ A mix of different CU versions is ok.
○ A mix of Standard and Enterprise editions is ok.
○ But cannot mix different major versions, such as 2013 and 2016.
What is a Database Switchover?
An administrator (human) -initiated move of active database copy.
The database copy that was previously the “active copy” is dismounted and becomes a passive copy.
Then, another copy that had previously been passive is mounted and becomes the active copy.
How are database copies utilized within a DAG?
For any given database, one DAG member has a copy of it which is designated as the “active copy” of that database. A database only has one active copy at a time.
The active copy is the one that is mounted and servicing clients.
Passive copies exist on other DAG members, are not mounted, and are updated via continuous replication.
You can have up to 15 passive copies of a database (across 15 other DAG members.)
What does it mean to “Activate” a database copy?
Switch it from being a passive copy to the active copy (and simultaneously dismounting the previously active copy to make it passive).
It’s another term for a Database Switchover.
What is a Database Failover?
A system-initiated (automatic) move of active database copy in response to a fault, such as a disk or server failure.
Essentially, the same thing as a Database Switchover, except it happens automatically.
What is a CAAP?
Cluster Administrative Access Point
A computer account with a single IP address that serves as an administrative access point for a DAG.
Exchange 2016 can use a CAAP, however, it defaults to not using it.
What are the disadvantages of using CAAP?
It makes management a little more complicated, and introduces two failure domains: a potential for IP address conflict, and a computer account which could be disabled or deleted.
When setting up a dedicated DAG replication network, what settings are required for Auto-Configuration to work?
- Do not configure a DNS server or Gateway on the Ethernet Adapter.
- In TCP/IP Settings > Advanced > DNS > uncheck “Register this connection’s address in DNS”
- Disable “File and Printer Sharing for Microsoft Networks”
- Disable “Client for Microsoft Networks”
Provide an example PowerShell command for adding an Exchange Server to a DAG.
(Answer has line breaks inserted for readability.)
Add-DatabaseAvailabilityGroupServer
- Identity
- MailboxServer
How many IOPS will a database copy have when it is a passive copy, in comparison to what it will have as an active copy?
About 50%
What is an Activation Preference?
A property of database copies.
It indicates the administrator’s preference for which database copy is most prefered to be active.
It is considered by Active Manager during failovers and targetless switchovers, but it is not the only deciding factor.
A database will have a preference number set for each server that hosts a copy of it. For example, a DAG with four members will have a preference of 1, 2, 3, and 4 assigned to each server for each database.
What is a targetless switchover?
An manually (administratively) initiated event where a database copy is changed from active to passive, and another database copy will become active, without specifying which copy to activate.
It’s a Database Switchover, except the database copy to activate is not specified.
Active Manager will determine which copy to activate.
What is the “PreferenceCountList” property of a DAG member, and how is its data formatted and understood?
It shows how many databases it has set to different Activation Preference levels.
It is displayed in this format:
{2, 3, 0, 1}
The above example indicates that this server has:
- 2 database copies with Activation Preference 1
- 3 database copies with Activation Preference 2
- 0 database copies with Activation Preference 3
- 1 database copies with Activation Preference 4
How can Azure be utilized for multi-site DAGs?
You can have a File Share Witness (FSW) in Azure as a “third-site” FSW, which provides a quorum no matter which other site may fail.
What is DAC Mode?
Datacenter Activation Coordination Mode
A property of DAGs designed to prevent split-brain conditions when DAG members become isolated.
