An Exploration of FlexVols that Underlay VMware Datastores

This post is a continuation of the series that I started with aggregates. FlexVols are created inside of an aggregate and are the logical assignment of the aggregate’s capacity to sub-containers. Think of a FlexVol as a folder on a file system with a quota applied to it…while that isn’t technically true, it get’s the gist across.

FlexVols are the data containers from which CIFS/NFS data (including virtual machines) is served, and/or LUNs are hosted from. They are the functional level for which many features are applied, such as deduplication, and provide logical separation for data sets. From a security point of view, no data in one volume is available from another, and even though the disks are shared, there are no shared blocks between volumes (even with deduplication).

Clustered Data ONTAP introduced the ability to move volumes between nodes in the cluster. I won’t preach about the benefits of cDOT, but there are many and they far outweigh the added complexity. This series is meant to stay focused on the data container settings, which are the same between 7-Mode and clustered Data ONTAP.

Before we begin, I want to note that TR-3749 and TR-4068 should always be the primary reference and guide when deploying VMware using NetApp storage.

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An Exploration of Aggregates that Underlay VMware Datastores

NetApp storage, much like ogres and onions, is made up of several layers. Regardless of using Data ONTAP 7-Mode or clustered Data ONTAP (cDOT), there are always aggregates which contain volumes which contain NFS/CIFS shares and/or LUNs. Aggregates are the physical grouping of disks into RAID groups on which all data is stored when using Data ONTAP, they are the foundation on which everything else rides.

Storage Layers

I am going to start examining those configurables which may, or may not, be important when hosting virtual machines. This will be broken into several parts, one for each of the layers:

All of these components are configured similarly with both 7-Mode and C-Mode. C-Mode adds another layer of abstraction, known as the Storage Virtual Machine, which enhances data mobility and manageability on the storage array, but that does not affect the settings on the actual data container constructs.

Each of these entities has configuration options and settings that can be tweaked, tuned, and adjusted for various scenarios. The defaults for these settings are conservative and capable of meeting a broad range of requirements, but they can also be changed to meet a variety of more specific needs for capacity, performance, ease of management, etc. Remember, just because a setting can be adjusted doesn’t mean that it needs to be. All environments are different, and there is rarely only a single “correct” way to configure your storage.

Before we begin, I want to note that TR-3749 and TR-4068 should always be the primary reference and guide when deploying VMware using NetApp storage.

Read more

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