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High Availability

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The Hard Truth About Patching SQL Server Availability Groups (Hotfixes, Cumulative Updates, and Service Packs)

Kendra Little
Always On Availability Groups, Breaking News
46 Comments
Whoa, be careful with that fix As a DBA, you’re responsible for identifying necessary updates to keep your SQL Servers healthy. Your business may have some mandates about the frequency of patches, but even if they don’t, you have a duty to look out for Cumulative Updates, Service Packs, and out of band hotfixes that can prevent…
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Failing over an Asynchronous Mirror in SQL Server (video)

Kendra Little
Database Mirroring
5 Comments
Will a long running open transaction block you from changing to synchronous mode and failing over to your SQL Server database mirror? Join Kendra to test performing a planned failover from an asynchronous database mirror. Brent Says: Often, when I’m working with developers, they’re totally surprised that SQL Server’s failover methods all break in-flight transactions. No matter…
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Urgent AlwaysOn Availability Groups Bug

Brent Ozar
Always On Availability Groups, Breaking News, SQL Server
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4 Comments
If you’re using AGs, don’t apply these patches: SQL 2012 SP2 CU3 SQL 2012 SP2 CU4 SQL 2014 CU5 until you read this Microsoft post about a breaking bug. Your AG may stop synchronizing due to blocking between user queries and a system session. The fix is to disable automatic failover, restart the primary, and…
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How Would You Change Always On Availability Groups?

Brent Ozar
Always On Availability Groups, SQL Server
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88 Comments
SQL Server 2012 introduced AlwaysOn Availability Groups, a way to achieve high availability, disaster recovery, and scale-out reads. SQL 2014 brought some improvements around higher uptime and more scale-out, and all signs point to continued improvements in the next version of SQL Server, too. (I love it when Microsoft brings out features like this and…
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What Amazon RDS for SQL Server Users Need to Know about Multi-AZ Mirroring

Brent Ozar
Amazon Web Services (AWS), Database Mirroring
9 Comments
Amazon Relational Database Service (RDS) now supports multi-availability-zone SQL Servers. This means you can have a primary database in one data center, and a secondary replica in another data center. Those Portland folks were always a little bit backwards anyway. When your primary server goes down, OR when the entire AZ goes down, you can fail…
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Careful Adding Indexes with Always On Availability Groups

Brent Ozar
Always On Availability Groups, SQL Server
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8 Comments
In theory, you can add indexes online with SQL Server Enterprise Edition. In theory, with AlwaysOn Availability Groups, you can add and drop indexes on the primary replica whenever you want. In theory, you can perform read-only queries on the secondaries whenever you want, and nobody gets blocked. In practice, these things don’t always add…
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Auto-Scaling SQL Server Always On Availability Groups with Virtualization

Brent Ozar
Always On Availability Groups, Amazon Web Services (AWS), Virtualization
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8 Comments
Time for a thought exercise. Thought exercises are hard. You’ve got a database application that has bursty and unpredictable loads. Out of nowhere, you’ll suddenly get socked with a large amount of SELECT queries. Due to the way the app is written, you can’t cache the query results – the queries keep changing, and the business…
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Always On Availability Groups, Backup Checksums, and Corruption

Brent Ozar
Always On Availability Groups, SQL Server
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14 Comments
The latest version of sp_Blitz® alerts you if you haven’t been using the WITH CHECKSUM parameter on your backups. This parameter tells SQL Server to check the checksums on each page and alert if there’s corruption. But what about corrupt backups? Books Online says: NO_CHECKSUM – Explicitly disables the generation of backup checksums (and the validation…
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Update on Stack Overflow’s Recovery Strategy with SQL Server 2014

Brent Ozar
Always On Availability Groups, Stack Overflow
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2 Comments
Back in 2009 (wow, seems like only yesterday!), I wrote about designing a recovery strategy for Stack Overflow. Back then, I wrote: With these answers in mind, Stack Overflow’s decisions not to do transaction log backups, offsite log shipping, database mirroring, and so on make good business sense. Us geeks in the crowd may not like it,…
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Common SQL Server Clustering, AlwaysOn, and High Availability Answers

Brent Ozar
Always On Availability Groups, Clustering, SQL Server
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Our live webcast topic this week was Q&A – you could bring any HA/DR questions, and we could avoid your answers. Just kidding. Here’s the webcast – we apologize for the audio, WebEx is still getting their act together. It cleans up after the first couple of minutes. And here’s the questions we couldn’t get…
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Log Shipping FAQ

Jes Schultz
Log Shipping, SQL Server
364 Comments
I’ve been working with and talking about SQL Server Log Shipping a lot lately! One way to ship logs… I’ve gotten a lot of great questions about log shipping, so I’ve put together an FAQ. What editions of SQL Server is log shipping available in? 2012 – Enterprise, Business Intelligence, Standard, and Web 2008R2 –…
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VMware HA is Not Database Server High Availability

Brent Ozar
Clustering, SQL Server, Virtualization
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13 Comments
I served with High Availability. I knew High Availability. High Availability was a friend of mine.  VMware HA, you’re no High Availability. See, for us database administrators, high availability means protection when: The system drive fills up because some potato decided to download a bunch of files An operating system or database server update goes…
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Why Your SQL Server Cluster Shouldn’t Be Virtualized

Brent Ozar
Clustering, Virtualization
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66 Comments
When people buy my virtualization training video, one of the followup questions I get most often via email is, “Can I build SQL Server clusters in VMware and Hyper-V?” In theory, yes.  Microsoft’s knowledge base article on SQL Server virtualization support says they’ll support you as long as you’re using configurations listed in the Server…
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