Coming a little late but saying something is not a best practice is not to say it isn't an perfectly acceptable practice. It is more a matter of business and environmental requirements, the level of your staff's technical ability, host and storage hardware capabilities, etc. In some environments, sharing datastores across clusters will be a bad idea while ideal for others.
You're correct FirstByte that in the design situations you descibe isolating datastores with their clusters makes sense. However, your cluster separation may be driven only by licensing or hardware (i.e. EVC baselines). In these cases, sharing storage across datastores may be preferred and possibly simplify configuration.
For small to medium 4.x and earlier environments, providing you understand the configuration maximums, locking thresholds, and storage hardware capabilites, sharing datastores is perfectly acceptable. As environments get much larger this, of course, deserves closer scrutiny.
Duncan: With respect to sharing datastores in 5.x, a colleague did point out this "Clustering Technical Deepdive" quote with respect to sharing datastores (below with my questions).
Chapter 3 - Fundamental Concepts" and it is determined by the redesign of the HA stack (master/slaves). The master on each cluster will try to take ownership of all the datastores it can access. This will introduce a risk factor in case of an HA event.
Basic Design Principle
To maximize the chance of restarting virtual machines after a failure we recommend masking datastores on a cluster basis. Although sharing of datastores across clusters will work, it will increase complexity from an administrative perspective."
- What is the introduced risk factor you refer to at the end of the first staement?
- Can you explain "maximize the chnace of restarting virtual machines after failures" and how it relates to shared datastores?
- With versions of ESX 4.x an earlier, I personally found it less complex administratively to share datastores across clusters at least no more complex. Can you expound on that a bit.