Although most Virtual SAN design and sizing exercises are straightforward, careful planning at the outset can avoid problems later. Based on observed experiences to date, the most frequent design issues are:
- Failing to use VCG-listed components, drivers and firmware, resulting in unpredictable behavior. Flash devices and IO controllers are particularly sensitive.
- Not properly sizing cache for capacity growth (e.g. thin volumes progressively getting fatter), resulting in declining performance over time.
- Using 1Gb networking for performance-intensive environments, with predictably poor results.
- Not understanding 3-node limitations associated with maintenance mode and protection after a failure.
- Using very large, slow disks for capacity, resulting in poor performance if an application is not cache-friendly.
- Failure to have sufficient extra capacity for operations.
