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One of the key components of the software-defined data center is storage, and VMware's answer to a traditional storage array was unveiled in March with its Virtual SAN (VSAN) feature. Using VSAN allows a business to pool storage from several servers to provide a highly available data store for VMs. While a relatively new feature, it has piqued the interest of many administrators looking for a cheaper way to handle storage.
SearchVMware talked with Duncan Epping, chief technologist in VMware's CTO office and one of the authors of the book Essential Virtual SAN: Administrator's Guide to VMware VSAN, about VSAN and which features may appear in the next version.
What do you think is the biggest advantage a virtual storage appliance has over a traditional storage system?
Duncan Epping: In my opinion, the advantage a VSA or VSAN solution has over traditional storage definitely is the flexibility and agility the architectures typically offer. Scaling out instead of scaling up is another advantage, as well as offering resources in a simple fashion.
Will the next version of VSAN change how SSDs are used?
Epping: As announced during VMworld, with the next version of VSAN it is even possible to use SSDs as the capacity layer. This will definitely change the way people will use flash in their data center and will lead to even higher-performing VSAN infrastructures.
What happens if one of the SSDs fails? Will performance suffer?
Epping: If an SSD fails, the impact is determined by the I/O pattern and the size of the working set. As you lose your write buffer and the read cache for those disks within the disk group, it is likely that you have temporary performance degradation. However, if blocks are accessed on another host, then they will also be cached there over time.
VMware has been pushing storage policy-based management, but are there drawbacks to handling storage this way?
Epping: In my opinion, there are no direct drawbacks other than that customers will need to change their operational procedures based on this new way of provisioning and managing virtual machines. It will take some time to get used to, but as everything is fully integrated with vSphere, the change is easy for most people and it brings a lot of operational efficiency.
What are your recommendations for a company that wants to use VSAN for tier-one workloads?
Epping: My recommendation would definitely be to think through the design and to consider things like having multiple disk groups per host instead of a single disk group. [The] reason for this is that more disk groups will give you more failure domains, and it will limit the number of objects impacted when an issue has occurred.
What are some customer requests you've had for future versions of VSAN? Which have the most likelihood of materializing?
Epping: I have received a lot of requests for all-flash VSAN and this is, as mentioned earlier, also something that VMware will bring in the near future.
Another question that comes up often is stretched deployment support for VSAN. This is not something that VMware has announced, but I would expect that it is something that will be looked at in the future.
Also, support for JBOD devices is something that comes up regularly, especially with those customers using blade systems. This is something that was also discussed at VMworld, but no specifics were given. That means which devices that are supported is still up in the air and we will have to wait until more info is released by the VSAN team.