1. AlwaysOn Mirroring, Clustering
What are they?
What are they not?
Who Cares?
Don Conrad
MCP, MCDBA,
MCITP(SQL 2005/2008),
MCSE Data Platforms,
OCP
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2. WHAT ARE They? AlwaysOn, Mirroring, Clustering
Each makes data more available for reporting purposes than it might otherwise be.
Two of these safeguard primary data by providing nearly instantaneous copies elsewhere.
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3. Primary data in alternative location.
AlwaysOn
Provides primary data available in alternative location(s).
Fully, or near-fully synchronized, depending on the configuration. Read-only, or no-read.
Relieves primary server Load
Hot-standby server(s)
Mirroring
Primary data in alternative location.
Warm standby server and data
Synchronized data
No-read data
Automatic or manual failover
Automatic failover requires third server
Clustering
Hot standby server
One primary data set
Automatic failover
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4. AlwaysOn Requirements
Minimum of two sets of servers and storage,
One additional set of server/storage for each additional replica
Equal drive configuration for the replicas.
One license for SQL Server 2012 for each server
(One exception: if there’s only one secondary replica and
it’s not to be in read-only mode,
it needs no license)
Windows Enterprise server on each server(for the clustering)
Windows Failover Clustering on each server
Additional network names and ips for the various components
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5. AlwaysOn Requirements
Cont’d
A network file share accessible by servers.
All SQL Service accounts must be local admin to it
Decisions on the various configurations: Clustered servers
listeners, read-only, back ups, latency, quorum votes etc s
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6. AlwaysOn Architecture(
WorkStation
Public Net
Public Net
Public Net
Server 1
Server 2
Server 3
Primary
Initial entry
Secondary
readable
Secondary
Not readable
Log
Log
Log
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7. AlwaysOn Availability Group ( WorkStation Server 2 Server 3 Public Net
read-write
Data Base
Availability Group r
Server 2
Server 3
Read-only
No-read 7
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11. Configuring Availability Group Listener
AlwaysOn
Configuring Availability Group Listener
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12. AlwaysOn Configuration Considerations
Latency: Synchronous vs. Asynchronous should respond to the amount
of allowable data loss
If replicas are Read-only, must use SQL code or Power-Shell to enable
applications to access via connection strings, i.e. “read-intent”.
Quorum votes need to be determined. The quorum is virtual, not on a separate partition
Production backups, log-shipping, replications, checkdbs etc
can be moved to the secondary replicas off of production
Primary server can be clustered for hardware redundancy
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13. Mirroring Two Servers Connected Via Ethernet Primary server is active.
Mirror server passive, data not accessible.
Mirror server contains a restored copy of a backup from primary database, restored database is kept in recovering mode until it becomes the primary server.
Primary server sends all transactions to secondary server. These are applied synchronously i.e. immediately. Confirmation is sent to primary server before the transaction is committed.
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14. Mirroring failover types
Automatic failover
requires a third server called the Witness server
Manual failover
requires only two servers, principal and mirrored
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15. Mirrored Topology --Automatic Failover(
WorkStation
Public Net
Data
Data
Node 1
Node 2
Primary storage
Log
Log
Mirrored storage
Witness server
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16. Clustering
Clustering involves one or more active servers, and one standby server connected via ethernet
Primary server health is monitored via software in a quorum drive.
Standby server is fully configure as a SQL Server
If quorum detects an active server failure, switches the related data drives to the standby server, sends alerts
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17. Active-Passive Node 1 active
Clustered Topology
Active-Passive Node 1 active
WorkStation
Public Net
Node 2
Node 1
Shared storage
Private Net
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18. Active-Passive Node 2 active
Clustered Topology
Active-Passive Node 2 active
WorkStation
Public Net
Node 2
Node 1
Shared storage
Private Net
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19. Resources required Item Hard$ Soft$ Data Protect?
AlwaysOn servers Ent Licenses %
2+ storage
Mirroring server Licenses %
Clustering Server license none
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20. Data does not exist in a vacuum.
WHY?
Data does not exist in a vacuum.
It must be accurate.
It must be used to be beneficial.
To be used it must be available:
in a manner timely enough to enable appropriate decisions to be made in a timely manner;
in a manner that encourages users using it via our tools, there’s always the O----- factor;
quickly enough that users don’t become frustrated.
AlwaysOn, Mirroring and Clustering further those goals.
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21. Users rely on us to provide accurate, timely data.
WHO CARES?
WE DO.
Users rely on us to provide accurate, timely data.
Each of these techniques either safeguards data or expedites its usability.
Each has its benefits,
and costs.
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22. Replication Three types
1. SnapShot– Selected tables and data are copied to subscriber. Data is frozen, not updated.
2. Transactional—Selected tables are copied to subscriber(s); tables, indexes, data are transferred. Per synch schedule all new, committed transactions to primary table(s) are posted to subscriber based on un-replicated transactions in publisher’s log file.
3. Merge—tables, data are copied to subscribers. Updates by either subscribers or publishers are copied to the other. Rules exist to resolve conflicts.
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23. Replicated Topology: Transactional (
WorkStation
Direct connection not guaranteed
Public Net
Public Net
Data
Committed Transactions/ re-synch
Node 1
Node 2
Publisher
Log
Log
Subscriber
Data is inserted in one direction, Per re-synch schedule (Once per…to continuous). Once inserted, Data is not changed.
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24. Replicated Topology: SnapShot (
WorkStation
Direct connection not guaranteed
Public Net
Public Net
Data
snapshot
Node 1
Node 2
Publisher
Log
Log
Subscriber
Data is inserted in one direction, once. Once inserted, Data is not changed.
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25. Replicated Topology: Merge
Replicated Topology: Merge. Typically multiple subscribers, limited new data (
WorkStation
Direct connection not guaranteed
Public Net
Public Net
Data
Committed Transactions/ re-synch
Node 1
Node 2
Publisher
Log
Log
Subscriber
Data is inserted in both directions, publisher to subscriber, then vice-versus per re-synch schedule. Sequences, conflicts are decided on rules.
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26. SnapShot Three Meanings
1. Replication– Selected tables and data are copied to subscriber. Data is frozen, not updated.
2. Copy—Virtual copy is instantaneously produced of entire subject database. Physically exists as pointers to non-updated PAGES, not tables. When page is updated, initial page is instantiated, frozen. Can always duplicate initial data unless primary files are damaged.
3. Transaction Isolation level —new with 2008, beyond this discussion.
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27. summary Clustering Server Licenses Other none
Mirroring server Licenses arcane know % 27
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28. summary Clustering, log-shipping, mirroring, replication and snapshots
All offer alternatives means of accessing primary data.
Each has costs and benefits.
Each can be useful depending on the nature of the data & how it’s used
No one fits all needs. Each might be useful.
User needs will determine which is beneficial.
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