What HADR Option(s) Are Right For You?

Where’s The AlwaysOn?

Levels of Protection InstanceDatabaseObject Availability Groups  FCI Log Shipping  Mirroring  Replication (Merge)  Replication (P2P) 

Options Per Version /R Availability Groups  FCI Log Shipping Mirroring  Replication (Merge) Replication (P2P) 

SQL 2000 Options By Edition WorkgroupStandardEnterprise FCI*  Log Shipping Replication (Merge) * 2 nodes only in Standard

SQL 2005 Options By Edition WorkgroupStandardEnterprise FCI*  Log Shipping Mirroring**  Replication (Merge) Replication (P2P)  * 2 nodes only in Standard ** High safety (synchronous) only in Standard

SQL 2008 / 2008 R2 Options By Edition WebStandardEnterpriseDatacenter FCI*  Log Shipping Mirroring**  Replication (Merge)*** Replication (P2P)  * 2 nodes only in Standard ** High safety (synchronous) only in Standard *** Web only supported as subscriber

SQL 2012 / 2014 Options By Edition WebStandardBIEnterprise Availability Groups****  FCI*  Log Shipping Mirroring**  Replication (Merge)*** Replication (P2P)  * 2 nodes only in Standard/BI ** High safety (synchronous) only in Standard/BI *** Web only supported as subscriber **** Up to 4 secondary replicas in secondary replicas in 2014

Failover Cluster Instances (FCI)  You might also might know it as Clustering  Common Terms:  Active/Active or Active/Passive (not correct use N or N+1)  MSCS (Microsoft Clustering Services) – Windows NT4.0 to 2003  WSFC (Windows Server Failover Cluster) – Windows 2008 and up  Full copy of SQL installed on all servers (nodes)  Transparent client redirection on failover*  Jobs, logins, linked servers, etc… also failover  Some special hardware requirements  Shared storage or 3 rd party hardware solution  There are single points of failure

Log Shipping  Not HA technology, but critical for business continuity  Scheduled backups of transaction logs get moved and restored to other servers  Can delay applying of logs on other servers  Perfect for those “OH moments  Possible to use built in routines, or roll your own  Great for remote DR  Limited to databases only.  Logins, jobs, connection strings, etc.. Have to be managed  Client redirection manual or via DNS

Mirroring  Deprecated, but doesn’t look like it’s going away any time soon  May not live past SQL 2016 with AG support in Std Edition  Two different modes  High Safety (2 phase commit)  High Performance (Enterprise Edition only)  Provides automatic failover (with Witness)  Transparent client redirection (use Failover Partner in conn string)  Single database in mirror  Have manage failover for multiple databases  Have to manually manage logins, jobs, linked servers, etc…  Can only have a single mirror  Has no domain requirements

Merge Replication  Object level, so very restrictive  Requires conflict resolution which can impact performance  Can develop custom resolvers  Needs a GUID on each row, impacts storage  Does not scale well to high transaction levels  Not a good choice

Peer to Peer Replication  Object level, so very restrictive  Need to very carefully manage ranges at each location for peer writes to prevent serious database issues  Using multi-site, multi-write can allow for local scale  Management can be very complicated

Availability Groups  Built on WSFC (to manage quorum) so requires AD  Sends transactions over to secondary replicas  Synchronous mode (allows for automatic failover)  Asynchronous mode (great for offsite DR)  Allows reading from secondary replicas  Incurs a 16-byte per row overhead on Insert/Update  4 secondary replicas in 2012, 8 in 2014  Multiple databases allowed in an AG  Requires manual management of logins, jobs, linked servers, etc…

Availability Groups Are The New Big Shiny  They can be a (reasonably) easy way to get HA going without specialized hardware, but…  Multiply the storage costs, as you’ll be paying per server  Reading off a secondary? That’ll cost you  Multi-subnet configuration can lead to management nightmares  SQLPS, SSMS do not support the MultiSubnetFailover connection option  Sync commit mode can inhibit performance  No cross database or DTC transactions (coming in SQL 2016!)  Will only work within a single domain and WSFC  Lose the WSFC or AD and lose the AG  Do NOT have AGs as your sole HADR option!

HADR With AGs and…?  First option… Log Shipping  Provides ability to delay logs application to secondary server  Secondary can reside outside the WSFC  Second option… FCI  Provides initial instance level protection  Cannot automatically failover to another node in AG  Third option… Log shipping & FCI  Best of both worlds, but…  No automatic failover within the AG

Questions?