Most companies have virtualized their servers and stored their virtual machines on shared storage. In most cases, that shared storage is a traditional SAN or NAS where those VMs are treated just as any other data block. While this has worked well in general, over time, enterprises have realized that there are a number of inefficiencies with this design.
Those inefficiencies include:
- Problems with VM I/O operations such as cloning, snapshotting and provisioning from a template;
- Poor performance because of the random workloads generated by the virtualized workloads (
- I/O blender effect); and
- Lack of per-VM storage statistics, which results in poor decision-making related to storage.
Enterprises, hypervisor vendors and storage vendors agree that there may be a better way to approach virtual machine storage.
Features of virtualization-aware storage
To respond to these inefficiencies, almost every storage vendor that claims to support virtualization has been adding features and functionality to make its offerings "virtualization-aware."
As usual, the meaning of "virtualization-aware" can become blurred as vendors promote their products, so let's define the requirements of true virtualization-aware storage. To be virtualization-aware, the storage system must:
- Receive information from the virtualization management platform to learn about the virtual machine storage.
- Send information to the virtualization management platform to help it make smart decisions and be more efficient.
Such features allow for ultra-fast I/O procedures like copying, cloning and snapshotting VMs. They also provide visibility into the storage layer on a per-VM basis, for both the admin and the management software.
Technology options that include virtualization-aware storage features can be broken down into the following categories, which we'll discuss in more detail later:
- Traditional physical SAN
- Software-defined storage
- All flash and hybrid arrays
- Hyperconverged solutions
There aren't any downsides to having such features in your storage unless, for some reason, your storage doesn't support traditional physical server workloads once it's virtualization-aware. Small and medium-sized businesses may enjoy the virtualization-aware feature set, but they will also likely need storage that supports physical, directly connected servers.
The other consideration here is the cost of virtualization-aware storage. Before opting for new features, find out whether the storage vendor requires a significant upcharge.
VMware responds to virtualization-aware needs
Over the past few years, VMware has begun offering two different virtualization-aware application programming interfaces (APIs) that storage vendors have the option to support. They are vSphere Storage API for Storage Awareness (VASA) and vSphere Storage API for Array Integration (VAAI).
These APIs cover the two basic requirements of virtualization-aware storage, as defined above.
With storage that supports VASA, the array provides vCenter with details on health status, configuration, capacity and thin provisioning. With this information, vCenter can do things such as automatically placing a new virtual machine on "gold-tiered" storage like a Fibre Channel SAN.
With storage that supports VAAI, the virtualization management storage operations are offloaded so that storage operations happen faster and more efficiently.
VMware's new Virtual SAN (VSAN), currently in public beta, is built into the hypervisor and is virtualization-aware.
Storage vendors also provide virtualization-aware features
Storage vendors have added support for VASA and VAAI in just about every type of traditional SAN or NAS. However, there's more to networked storage being virtualization-aware than just VASA and VAAI.
Here are a few examples of storage vendors that offer virtualization-aware options:
- Tintri entered the market as the first virtualization-aware storage vendor and is still leading the pack in VM-aware features. The Tintri hybrid array delivers 99% of I/O from flash and delivers VMs via the Network File System. Management focuses on VMs, not logical unit numbers or volumes.
- Tegile, which offers all-flash storage arrays, has been steadily improving its virtualization-aware feature set by connecting its arrays to vCenter to offer per-VM statistics and VAAI offload.
- Vendors such Nutanix, Scale Computing and SimpliVity offer virtualization-aware storage in their hyperconverged solutions that merge compute, storage and virtualization. While this is innovative technology, remember that you would be deploying much more than just storage, so these products require a larger investment of time and money.
Choosing virtualization aware storage technology
No matter what size virtual infrastructure you have, virtualization-aware storage has its benefits. The challenge is weeding through the available products to select the best technology for your company.
As with any new data center tool, you should compare the pros and cons of each to find the best option. Perform the same kind of cost analysis that you would do for any storage system.
To evaluate virtualization-aware storage, ask yourself and potential vendors the following questions:
- What features does your current storage offer that could make it more virtualization-aware? Can you simply upgrade your current array and add new features like VAAI? In many cases, this may be just a firmware upgrade.
- Do you want the most advanced virtualization-aware storage, or is VAAI offload adequate? By going with what has become the standard in storage, VAAI, you can significantly improve performance, often without buying new storage.
- Are you in the market for an all-new hyperconverged solution that provides compute, storage and virtualization in one? Even though you may answer "No," consider the potential return on investment from replacing your current servers and SAN. In many cases, a hyperconverged system is approximately the cost of a SAN upgrade alone, and it includes compute and unified management.
- Would VMware's VSAN be right for your company's move to virtualization-aware storage? With VSAN in beta, it might be best to wait until the features and price are clarified, but it's worthwhile to evaluate VSAN as more information becomes available.
In the end, virtualization-aware storage is a great feature, but not all of the technology is of equal value. Ask vendors about the maturity of their products. If two storage vendors say that their storage is "virtualization-aware," their capabilities could be completely different. Always make sure that you see the features for yourself.
This was first published in March 2014