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VMblog.com: High Availability vSphere for SQL Server: 5 Things You Need to Know

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SQL Server administrators have many options for implementing high availability (HA) in a VMware environment. VMware offers vSphere HA. Microsoft offers Windows Server Failover Clustering (WSFC). And SQL Server in WSFC has its own HA options with AlwaysOn Availability Groups and AlwaysOn Failover Clusters.

Third party vendors also provide solutions purpose-built for HA and disaster recovery, and these often integrate with other solutions to create even more options. For example, some solutions leverage the AlwaysOn Failover Cluster feature included with SQL Server to deliver robust HA and data protection for less than the cost of AlwaysOn Availability Groups that require the more expensive Enterprise Edition.

This article highlights five things every SQL Server administrator should know before formulating a high availability strategy for mission-critical applications in a vSphere environment. Such a strategy is likely to resemble the multi-site configuration shown in Figure 1, which is not possible with some HA options.

1. High-Availability Clusters for vSphere require Raw Disk Mapping

The layers of abstraction used in virtualized servers afford substantial flexibility, but such abstractions can cause problems when a virtual machine (VM) must interface with a physical device. This is the case for vSphere with Storage Area Networks (SANs).

To enable compatibility with certain SAN and other shared-storage features, such as I/O fencing and SCSI reservations, vSphere utilizes a technology called Raw Device Mapping (RDM) to create a direct link through the hypervisor between the VM and the external storage system. The requirement for using RDM with shared storage exists for any cluster, including a SQL Server Failover Cluster.

In a traditional cluster created with WSFC in vSphere, RDM must beused to provide virtual machines (VMs) direct access to the underlying storage (SAN). RDM is able to maintain 100 percent compatibility with all SAN commands, making virtualized storage access seamless to the operating system and applications which is an essential requirement of WSFC.

RDM can be made to work effectively, but achieving the desired result is not always easy, and may not even be possible. For example, RDM does not support disk partitions, so it is necessary to use “raw” or whole LUNs (logical unit numbers), and mapping is not available for direct-attached block storage and certain RAID devices.

2. Use of Raw Disk Mapping means Sacrificing Popular VMware Features

Another important aspect of being fully informed about RDM involves understanding the hurdles it can create for using other VMware features, many of which are popular with SQL Server administrators. When these hurdles are deemed unacceptable, as they often are, they eliminate Raw Device Mapping as an option for implementing high availability.

The underlying problem is how RDM interferes with VMware features that employ virtual machine disk (VMDK) files. For example, RDM prevents the use of VMware snapshots, and this in turn prevents the use of any feature that requires snapshots, such as Virtual Consolidated Backups (VCBs).

Raw Disk Mapping also complicates data mobility, which creates impediments to using the features that make server virtualization so beneficial, including converting VMs into templates to simplify deployment, and using vMotion to migrate VMs dynamically among hosts.

Another potential problem for transaction-intensive applications like SQL Server is the inability to utilize Flash Read Cache when RDM is configured.

3. Shared Storage can create a Single Point of Failure

The traditional need for clustered servers to have direct access to shared storage can create limitations for high availability and disaster recovery provisions, and these limitations can, in turn, create a barrier to migrating business-critical applications to vSphere.

In a traditional failover cluster, two or more physical servers (cluster nodes) are connected to a shared storage system. The application runs on one server, and in the event of a failure, clustering software, such as Windows Server Failover Clustering, moves the application to a standby node. Similar clustering is also possible with virtualized servers in a vSphere environment, but this requires a technology like Raw Disk Mapping so that the VMs can access the shared storage directly.

Whether the servers are physical or virtual, the use of shared storage can create a single point of failure. A SAN can have a high availability configuration, of course, but that increases its complexity and cost, and can adversely affect performance, especially for transaction-intensive applications like SQL Server.

4. HA vSphere Clusters can be built without Sacrificing VMware Functionality

Some third-party solutions are purpose-built to overcome the limitations associated with shared storage and the requirement to use RDM with SQL Server’s AlwaysOn Failover Clusters and Windows Server Failover Clusters.

Figure 1 – A multi-site high-availability configuration protects applications from outages that affect an entire data center.

The best of these solutions provide complete configuration flexibility, making it possible to create a SANLess cluster to meet a wide range of needs – from a two-node cluster in a single site, to a multinode cluster, to a cluster with nodes in different geographic locations for disaster protection as shown in Figure 1. Some of these solutions also make it possible to implement LAN/WAN-optimized, real-time block-level replication in either a synchronous or asynchronous manner. In effect, these solutions are capable of creating a RAID 1 mirror across the network, automatically changing the direction of the data replication (source and target) as needed after failover and failback.

Just as importantly, a SANLess cluster is often easier to implement and operate with both physical and virtual servers. For example, for solutions that are integrated with WSFC, administrators are able to configure high-availability clusters using a familiar feature in a way that avoids the use of shared storage as a potential single point of failure. Once configured, most solutions then automatically synchronize the local storage in two or more servers (in one or more data centers), making them appear to WSFC as if it was a shared storage device.

5. HA SANLess Clusters deliver Superior Capabilities and Performance

In addition to creating a single point of failure, replicating data on a SAN can significantly reduce throughput performance in VMware environments. Highly transactional applications like SQL Server are particularly vulnerable to these performance-related factors.

Figure 2 – Testing of SQL Server’s AlwaysOn Availability Groups and SIOS #SANLess clusters shows the throughput advantage possible with replication techniques purpose built for high availability and high performance.

Figure 2 summarizes test results that show the 60-70 percent performance penalty associated with using SQL Server AlwaysOn Availability Groups to replicate data. These test results also show how a purpose-built high-availability SANLess cluster, which utilizes local storage, is able to perform nearly as well as configurations not protected with any data replication or mirroring.

The #SANLess cluster tested is able to achieve this impressive performance because its driver sits immediately below NTFS. As writes occur on the primary server, the driver writes one copy of the block to the local VMDK and another copy simultaneously across the network to the secondary server which has its own independent VMDK.

SANLess clusters have many other advantages, as well. For example, those that use block-level replication technology that is fully integrated with WSFC are able to protect the entire SQL Server instance, including the database, logons and agent jobs-all in an integrated fashion. Contrast this approach with AlwaysOn Availability Groups, which failover only user-defined databases, and require IT staff to manage other data objects for every cluster node separately and manually.

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About the Author

Jerry Melnick, COO, SIOS Technology Corp.

Jerry Melnick (jmelnick@us.sios.com) is responsible for defining corporate strategy and operations at SIOS Technology Corp. (www.us.sios.com), maker of SIOS SAN and #SANLess cluster software (www.clustersyourway.com). He more than 25 years of experience in the enterprise and high availability software industries. He holds a Bachelor of Science degree from Beloit College with graduate work in Computer Engineering and Computer Science at Boston University.

Storage Switzerland: Storage Q&A: High Availability for Data Centers of all Sizes

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SIOS Technologies and Storage Switzerland recently joined forces for a highly attended webinar. The attendees asked some outstanding questions about flexible HA and DR for virtual servers and cloud environments. Joining Storage Switzerland Founder and Chief Steward George Crump on the Webinar is Director of Field Engineering Tony Tomarchio from SIOS.

Question 1

“What are the connectivity requirements between two geographically dispersed data centers, such as bandwidth and latency, in order for your high availability solution to work?”

Tony: It all comes down to the workload that you need to protect. We don’t have a minimum requirement per se. It depends on the I/O activity on your system, specifically data rate of change, which is how rapidly your disks being written. Let’s say you have one server, which on average is writing 3MB/sec to disk. SIOS Software wants to replicate that data as fast as you write it to disk locally to replicate it out. You need to look at the servers you want to protect. In Windows this is very easy to do. You can pull up PerfMon, look at disk stats and let that run for some representative time period. That will tell you exactly how much bandwidth you need to support real-time replication.

As far as the latency aspect of this question goes, we support both synchronous and asynchronous replication. Generally, you would go with synchronous replication if you have a high-speed low latency network connection. Synchronous gives you maximum data protection and zero data loss because it’s a double commit. The write isn’t considered complete until it’s made it to both source and targets. But you do have to factor in the round trip latency between source/target as that will have an effect on your write performance.

If you have higher latency and you’re more performance sensitive, you might go with asynchronous. But you have to understand that in the event of a failure there could be some in flight data that might not make it from source to target. So there could be some data loss. That is the classic trade-off between synchronous and asynchronous.

To summarize, we don’t have a minimum requirement as far as bandwidth and latency. It really comes down to how busy your servers are, how rapidly they write to disk, what your performance tolerances are, and how much data loss, if any, you can withstand.

Question 2

“How are the SAN-less clusters beneficial in a VMware environment?”

Tony: If you deploy VMware, it’s got built-in features such as VMware HA. That is a partial solution from an HA perspective. If you look at what VMware HA does, it protects you against host failures. If a host fails, it reboots a virtual machine onto another physical host in the VMware cluster. If you have an issue with the networking or the application that’s inside the virtual machine, essentially the virtual machine is a block box and that type of issue won’t necessarily be protected. Adding on application level availability and clustering at the guest level can provide you with a higher level of availability.

The other challenge that I mentioned before with doing guest level clustering in that type of environment is that you have to pass the storage up to the virtual machine. Usually you’ll have to configure raw device mapping (RDM), and then you’ll lose things like VMotion. You’re giving up some virtualization features for HA, but with a SAN-Less cluster solution from SIOS you can have both. We’re doing everything from inside the guest. There are no specific changes you need to make at the hypervisor level.

Question 3

“What storage configuration provides the best HA?”

George: I’m a SAN guy. But clearly from a cost perspective, the ability to use external drives has to be appealing both from a cost and familiarity perspective. What is your stance on that?

Tony: Certainly SANs are robust and have a lot of redundancy, such as redundant controllers, disks and so on. But at the end of the day shared storage in your cluster represents a single point of failure. Again, it may not be a hardware failure. Many times it’s a configuration or user error that causes connectivity loss to the SAN that can take down your entire cluster.

By going to a SAN-less configuration, you’re eliminating storage as a single point of failure and achieving a higher level of availability.

If you already have made the investment in a SAN, I’m not saying don’t use it. You can certainly use existing storage and server resources that you have in your infrastructure. But if that’s the way you were clustering in the past, let’s say two servers and a SAN, you might consider adding a third node with it’s own independent storage. It could be a different SAN or it could be local storage. That way you’ve now got another node in the cluster so you can withstand one more host failure. You’re also eliminating storage as a failure point, so technically you’re stepping up one notch in the availability chain.

George: I wrote a paper on this and there was a section called, “What can go wrong with your SAN Array.”

One of the interesting things that can go wrong is most systems have a RAID or something going on to protect it in case of a drive failure. But one of the things I find that takes people off guard is what the performance is like while the RAID rebuild is happening. It typically leaves you with two choices. You can turn down the speed at which the rebuild is happening leaving you exposed for a longer period of time, or you can speed up the RAID rebuild which typically hurts the disk I/O performance.

It sounds to me that in your environment, I can fail to a separate stand alone system and let the RAID rebuild happen all by itself on a separate primary system. That would be able to work, wouldn’t it?

Tony: Yes, you could certainly do that if performance during that operation was a concern. Basically what happens at the physical level, like a RAID rebuild, is transparent to our software. That’s one of the reasons why you can mix and match servers.

One of the requirements with our Windows solution is that drive letters match and all of the volumes are the same size. Whether it’s a single disk or it’s a RAID 0, 1, 5 or 10, under the covers that are all transparent. So yes, if that was a concern, you could potentially failover to another node in the cluster and let everything run off of that while your RAID rebuilds on the other side.

Question 4

“Can you use your software for anything other than SQL?”

Tony: Yes, you can use it with any cluster-able service or application. Most commonly we’re protecting SQL. We have solutions for Linux where we do a lot of SAP, Oracle and NFS type clusters. It’s really all over the map.

We can also protect custom applications. That is one of the benefits of having a block level replication technology. It is server, storage and even application agnostic. You just tell us which partitions or volumes you want to replicate and whatever data happens to live in there and we’re going to protect. From that regard, this can be used for much more than just SQL.

Question 5

“How is application performance impacted by running the SAN-less software?”

Tony: This comes back to the mode of replication. We support both synchronous and asynchronous replication. With asynchronous replication, you’re not going to see any kind of performance impact. If synchronous, then you’re only going to see an impact on writes to disk because it’s a double commit. Reads are not impacted.

If you go with synchronous replication, you’ll want to have a low latency network connection to minimize the overhead that synchronous replication imposes on writes.

VI Briefing: SIOS SANLess Clustering Software Provides Epicure Selections with High Availability and Disaster Recovery Protection for Critical SQL Server Applications

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Epicure Selections deploys hybrid solution providing additional cost savings of running on-premises with the reliability and flexibility of running in the cloud

SAN MATEO, CA – January 20, 2015 – SIOS Technology Corp. (www.us.sios.com), maker of SAN and #SANLess clustering software products, today announced that Epicure Selections is using SIOS DataKeeper Cluster Edition software to easily and cost-efficiently provide HA and DR protection for its business-critical SQL Server applications without the complexity of building out a remote DR site or purchasing costly SQL Server Enterprise Edition licenses.

Epicure, Canada’s leading direct sales company, sells healthy, easy-to-prepare food products through a network of over 16,000 consultants.  Epicure relies on two websites for its critical business operations. Its public website provides product, company, and consultant enrollment information to customers and people interested in becoming a consultant. The internal website provides consultants with important product information and enables them to place orders.

The company uses two instances of SQL Server Standard Edition, one for each website running on a single server. “Our websites are vital to our business,” said Russell Born, senior network infrastructure administrator at Epicure.

As the company grew and expanded its products and services, the Epicure IT department needed to update and protect its business-critical websites from downtime. It decided to move both websites from a third-party hosted facility to its on-premises data center and Amazon Web Services. As part of this update, Epicure wanted an efficient, cost-effective way to provide high availability and disaster protection for both websites while continuing to run them on two instances of SQL Server Standard Edition.

Using SIOS SANLess clustering software, Epicure IT staff created a two-node cluster in an active-passive failover configuration that enables each SQL instance to failover independently. One cluster node is in the on-premises data center and the second node is in an instance of the AWS EC2 cloud. Epicure IT staff created the SIOS SANLess clusters and configured them using the software’s intuitive graphical user interface.

The SIOS software provides Epicure with an easy, cost-efficient way to provide HA and DR protection for its business-critical SQL Server applications without the complexity of building out a remote DR site or purchasing costly SQL Server Enterprise Edition licenses. “The SIOS software has allowed us to create a hybrid solution providing additional cost savings of running on-premises with the reliability and flexibility of running in the cloud,” said Born. “Knowing that a website outage will result in an automatic failover allows our IT Team to focus their attention on other priorities to strengthen our business.”

“Whether you want to protect applications in a physical server, a private cloud within an organization, in a public cloud or a hybrid cloud, you need to protect applications, like Windows SQL Server, from downtime if the cloud instance or the cloud provider fails,” said Jerry Melnick, COO, SIOS Technology.  “Epicure is using SIOS to provide a fast, easy way to deploy applications in a high availability environment in the cloud while continuing to use Windows Server Failover Clustering.  I applaud them for their use case and innovation and look forward to continuing to provide value to their HA and DR strategies.”

About SIOS Technology Corp.
SIOS Technology Corp. makes SAN and #SANLess software solutions that make clusters easy to use and easy to own. An essential part of any cluster solution, SIOS SAN and #SANLess software provides the flexibility to build Clusters Your Way™ to protect your choice of Windows or Linux environment in any configuration (or combination) of physical, virtual and cloud (public, private, and hybrid) without sacrificing performance or availability. The unique SIOS #SANLess clustering solution allows you to configure clusters with local storage, eliminating both the cost and the single-point-of-failure risk of traditional shared (SAN) storage.

Founded in 1999, SIOS Technology Corp. (www.us.sios.com) is headquartered in San Mateo, California, and has offices throughout the United States, United Kingdom and Japan.

Reuters: SIOS Clustering 101 Webinar Series Will Examine Best Practices in Maximizing SQL Application Availability in a VMware Environment

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SIOS Clustering 101 Webinar Series Will Examine Best Practices in Maximizing SQL Application Availability in a VMware Environment

SIOS Technology Corp. (www.us.sios.com), maker of SAN and #SANLess clustering software products, today announced that the next session in its Clustering 101 webinar series featuring Microsoft Clustering MVP Dave Bermingham will examine high availability clusters in VMware environments.

Titled, “VMware Guest Based High Availability Clusters – Ways to Protect SQL and Maintain Flexibility,” this webinar will be held on Wednesday, January 28 at 10:00 AM PST / 1:00 PM EST. To register, please visit: http://us.sios.com/2015-01-clustering101/

This live, 30-minute webinar will address questions including: How do you maximize availability and comprehensively protect SQL applications in a VMware environment without sacrificing IT flexibility or important VMware features? Can you have a cluster and multisite replication with VMware? Participants can tweet their questions prior to the event to @SIOSTech using #Clustering101 or bring their questions and comments to the session.

David Bermingham is recognized within the technology community as a high availability expert and has been honored by his peers by being elected to be a Microsoft MVP in clustering since 2010. David’s work as director, technical evangelist at SIOS Technology Corp., has him focused on Microsoft high availability and disaster recovery solutions as well as providing hands on support, training and professional services for cluster implementations. David holds numerous technical certifications and draws from more than twenty years of experience in IT, including work in the finance, healthcare and education fields, to help organizations design solutions to meet their high availability and disaster recovery needs. Learn more at www.us.sios.com

About Clustering 101

Clustering 101 is a webinar series hosted by Microsoft MVP Dave Bermingham focused on addressing the numerous facets of clustering for high availability and data replication. Webinars in this series are held the fourth Wednesday of every month at 10:00 AM PST / 1:00 PM EST. Check the SIOS website for details: http://us.sios.com/about/news-events/

About SIOS Technology Corp.

SIOS Technology Corp. makes SAN and #SANLess software solutions that make clusters easy to use and easy to own. An essential part of any cluster solution, SIOS SAN and #SANLess software provides the flexibility to build Clusters Your Way™ to protect your choice of Windows or Linux environment in any configuration (or combination) of physical, virtual and cloud (public, private, and hybrid) without sacrificing performance or availability. The unique SIOS #SANLess clustering solution allows you to configure clusters with local storage, eliminating both the cost and the single-point-of-failure risk of traditional shared (SAN) storage.

Founded in 1999, SIOS Technology Corp. (www.us.sios.com) is headquartered in San Mateo, California, and has offices throughout the United States, United Kingdom and Japan.

SIOS, SIOS Technology, SIOS DataKeeper, SIOS Protection Suite, Clusters Your Way, and associated logos are registered trademarks or trademarks of SIOS Technology Corp. and/or its affiliates in the United States and/or other countries. All other trademarks are the property of their respective owners.

Winkowski Public Relations, LLC for SIOS
Beth Winkowski, 978-649-7189
bethwinkowski@US.SIOS.com

CNBC: SIOS Clustering 101 Webinar Series Will Examine Best Practices in Maximizing SQL Application Availability in a VMware Environment

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SIOS Technology Corp. (www.us.sios.com), maker of SAN and #SANLess clustering software products, today announced that the next session in its Clustering 101 webinar series featuring Microsoft Clustering MVP Dave Bermingham will examine high availability clusters in VMware environments.

Titled, “VMware Guest Based High Availability Clusters – Ways to Protect SQL and Maintain Flexibility,” this webinar will be held on Wednesday, January 28 at 10:00 AM PST / 1:00 PM EST. To register, please visit: http://us.sios.com/2015-01-clustering101/

This live, 30-minute webinar will address questions including: How do you maximize availability and comprehensively protect SQL applications in a VMware environment without sacrificing IT flexibility or important VMware features? Can you have a cluster and multisite replication with VMware? Participants can tweet their questions prior to the event to @SIOSTech using #Clustering101 or bring their questions and comments to the session.

David Bermingham is recognized within the technology community as a high availability expert and has been honored by his peers by being elected to be a Microsoft MVP in clustering since 2010. David’s work as director, technical evangelist at SIOS Technology Corp., has him focused on Microsoft high availability and disaster recovery solutions as well as providing hands on support, training and professional services for cluster implementations. David holds numerous technical certifications and draws from more than twenty years of experience in IT, including work in the finance, healthcare and education fields, to help organizations design solutions to meet their high availability and disaster recovery needs. Learn more at www.us.sios.com

About Clustering 101

Clustering 101 is a webinar series hosted by Microsoft MVP Dave Bermingham focused on addressing the numerous facets of clustering for high availability and data replication. Webinars in this series are held the fourth Wednesday of every month at 10:00 AM PST / 1:00 PM EST. Check the SIOS website for details:http://us.sios.com/about/news-events/

About SIOS Technology Corp.

SIOS Technology Corp. makes SAN and #SANLess software solutions that make clusters easy to use and easy to own. An essential part of any cluster solution, SIOS SAN and #SANLess software provides the flexibility to build Clusters Your Way™ to protect your choice of Windows or Linux environment in any configuration (or combination) of physical, virtual and cloud (public, private, and hybrid) without sacrificing performance or availability. The unique SIOS #SANLess clustering solution allows you to configure clusters with local storage, eliminating both the cost and the single-point-of-failure risk of traditional shared (SAN) storage.

Founded in 1999, SIOS Technology Corp. (www.us.sios.com) is headquartered in San Mateo, California, and has offices throughout the United States, United Kingdom and Japan.

SIOS, SIOS Technology, SIOS DataKeeper, SIOS Protection Suite, Clusters Your Way, and associated logos are registered trademarks or trademarks of SIOS Technology Corp. and/or its affiliates in the United States and/or other countries. All other trademarks are the property of their respective owners.

Winkowski Public Relations, LLC for SIOS
Beth Winkowski, 978-649-7189
bethwinkowski@US.SIOS.com