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Microsoft Exchange Server 2013 : Designing a Successful Exchange Storage Solution (part 3) - Selecting the Right Storage Hardware, Storage Validation Using Jetstress

12/27/2014 3:47:50 AM
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Selecting the Right Storage Hardware

Now we can move on to selecting appropriate hardware for our requirements. There are many aspects to this decision, and the requirements that we have identified so far represent only a few of them. Often there may be a hardware constraint in your requirements, which mandates that you use a specific storage technology or vendor. This technology may not be ideal for use with Exchange but may align with the organization's overall storage strategy. In some cases, this strategy has been mandated for all services, regardless of their requirements or function, and it will be necessary to use a particular storage platform. The other scenario is that you have free choice regarding the storage platform for Exchange, but then you will need to narrow down your choices. How do you narrow down your options? This section will discuss both scenarios and how to deal with them.

COMPANY-MANDATED STORAGE PLATFORM

First, let's take on the scenario where your storage platform choice is fixed. Even though this decision has been made for you, you still have work to do. To start, you need to research the platform that has been designated. Begin this process by looking at the Exchange Solution Reviewed Program (ESRP) - Storage. Search for a submission from the same storage vendor and, hopefully, for the same platform that is to be used.

ESRP submissions vary in quality and the usefulness of the information provided, but they are almost always a great place to find specific configuration details for running Exchange on a particular platform. ESRP is grouped into versions that relate to the Exchange platform to which they apply:

  • Exchange Server 2007: ESRP - Storage v2.1
  • Exchange Server 2010: ESRP - Storage v3.0
  • Exchange Server 2013: ESRP - Storage v4.0

If you cannot find an ESRP submission, look on the manufacturer's website for Exchange-specific configuration recommendations.

Next, evaluate your disk type options and RAID group configurations. Not all storage platforms allow all configurations, and so it is vital that you understand what you can and cannot do. Then try to map the data that you obtained from the Exchange 2013 Server Role Requirements Calculator, and try to make it fit the platform. Often, the best way to do this is to run a combined storage design workshop with the storage team, in order to evaluate the options, and then try to tweak the calculator accordingly.

Once this process is complete, try to define a validation approach. This is generally a small deployment of servers and storage on representative hardware that can be used for Jetstress testing. The goal of the Jetstress testing will be to validate that the proposed solution is capable of meeting the requirements identified by the calculator. This is where the marketing nonsense stops and the fun begins!

FREE CHOICE OF STORAGE PLATFORM

Recall that, in the second scenario, you have full control over the storage platform. This is often more challenging for a design team. Now you have to come up with a process for evaluating storage platforms and their ability to meet your requirements. To this end, the first things to define are your specification requirements. These are common areas of comparison; the aim for most team members is to grade the platform from 1 to 10 (where 1 is very poor and 10 is perfect for the task).

Cost This is obviously a key aspect. However, it is vital to consider the total cost of the platform and not just the purchase price. What are the support costs? What about operator training expenses? What about installation and configuration costs? If possible, calculate the total cost of the platform over a period of time, for example, two or three years, and use this to compare the real costs of each platform.

Operations How easy or difficult is this platform going to be to operate? Can it be easily upgraded? Can parts be swapped out without affecting service? Try to determine a common set of operational processes that will be required, and grade each platform on a 1 to 10 scale for the ease with which these tasks can be completed.

Space Datacenter space is a primary concern for many customers. Space is an expensive commodity in most datacenters, and it should be taken into consideration for any new platform. Try to determine the rack space required per GB or per mailbox for each platform to aid in making a comparison.

Power This is another area of increasing concern for recent deployments. The more power that a device draws, the more heat it usually generates. This leads to more demand for datacenter cooling. When possible, calculate the power in kWh per mailbox or per GB for comparison.

Performance From an Exchange perspective, your performance requirements are defined in the Exchange 2013 Server Role Requirements Calculator. Can the platform meet your IOPS, throughput, and capacity requirements while remaining under your recommended I/O latency thresholds when tested with Jetstress? We generally suggest that you record a pass/fail for each platform here, where failed systems are either redesigned and retested or discarded in the process.

Storage Validation Using Jetstress

What is storage validation? Simply put, the goal of this process is to ensure that the storage platform is capable of meeting the demands of Exchange Server to service end-user requests in a timely manner. If the storage platform is incapable of meeting these demands, then the end-user experience will suffer. We know this from experience in the early days with Exchange Server 2003, where poor storage performance equaled poor Exchange Server performance.

There is an important aspect to the validation process that is rarely discussed, however, and that is that it must take place with a calibrated workload. A calibrated workload means that the test workload applied should be approved (calibrated) by the Exchange product group as not only being a representative one but also equal to the workload generated by Exchange Server. This point is important because it separates out tools that generate workload, such as Iometer and LoadGen, from tools that generate a defined and calibrated workload, such as Jetstress.

Sometimes, in a project where the design has been completed and the storage is failing to pass the Jetstress test, a storage team member will insist that Jetstress is not a good test because the requirements can be met with Iometer, and that's proof that Jetstress is broken. A slight variation on this occurs when a team will use LoadGen to simulate the expected production workload and find that it passes whereas Jetstress fails and thus will come to the same conclusion; that is, LoadGen passes where Jetstress fails and so Jetstress must be broken. Both situations are equally difficult to address since the explanation of the results is complex. By far the most compelling explanation is that Jetstress is a calibrated workload, and when used with the values derived from the Exchange 2013 Server Role Requirements Calculator, it represents the peak two hours of a working day as accurately as possible.

When it comes to storage validation, Jetstress is the only real tool for the job. Now let's see how it works.

JETSTRESS TEST PROCESS

The Jetstress test process itself is documented in the Jetstress Field Guide. This does not yet exist for Jetstress 2013; however, the general process outlined for Jetstress 2010 still applies. The test must be conducted as follows if it to be considered successful:

  • Meets or exceeds the database IOPS requirements identified within the calculator in normal conditions
  • Meets or exceeds the database IOPS requirements identified within the calculator in degraded (rebuild) conditions
  • Runs for a duration of two hours (strict mode test)
  • Runs for a duration of 24 hours (lenient mode test)
  • Completes all test runs with a status of Passed

A common area of confusion about these tests is the 2-hour vs. 24-hour test recommendation. Jetstress runs in strict mode when the duration is less than six hours. A completed test run in strict mode is required to be sure that the storage is meeting the performance requirements. The lenient mode relaxes some of the peak latency spike requirements, and it is intended for longer duration testing. The 24-hour test is recommended to ensure that the storage platform is capable of operating at peak workload for an extended duration, since several cases have been logged where performance deteriorates over time when a storage platform is operating at or near its limits. If a storage platform passes all of these Jetstress tests, experience shows that the design is then good to go.

BUILD-TIME VALIDATION

There is one more aspect to Jetstress validation work that is sometimes disregarded or overlooked, and that is build-time validation testing. Build-time validation testing involves running a Jetstress test on each production Mailbox server before it is accepted into production. When discussing this type of testing, the question often asked is, why bother with this test when we have already tested an identical solution in the test lab and it has passed? The answer is that, although the tests are the same, the purpose is different. Validation tests in the lab were designed to corroborate design assumptions and decisions about the storage platform. The build-time validation is designed to ensure that the hardware has been deployed and configured appropriately to meet the requirements, and it is operating according to expectations; that is, it is not faulty.

It is not unheard of for a storage platform to pass Jetstress with flying colors in the test lab, where it receives TLC from the vendor presales team, only to find out that it fails to pass the same Jetstress test in a production environment, where it has been deployed and configured by a completely different team. This can be addressed by adopting build and configuration standards. However, these are still not foolproof, and so adopting an automated Jetstress validation test prior to installing Exchange Server into a production environment is highly recommended. This recommendation is even stronger when a complex storage solution has been deployed. One thing to remember is that it is much easier to fix a problem when Jetstress is the only user of the service. If you first become aware of a problem when an end user reports it, your job becomes significantly harder.

 
Others
 
- Microsoft Exchange Server 2013 : Designing a Successful Exchange Storage Solution (part 2) - Making Sense of the Exchange Mailbox Server Role Requirements Calculator
- Microsoft Exchange Server 2013 : Designing a Successful Exchange Storage Solution (part 1) - Requirements Gathering
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