Just finished up a quick two minute video presented by my colleague, Jim Bahn, on how to solve the common problem of SAN oversubscription ratio problems. Interestingly I've found the oversubscription problem with just about every end user I've been to this last year, so there clearly is a lack of awareness on the issue.
The biggest limitation is that you cannot historically trend the ASIC or Blade utilisation of a SAN Director with its native tools. I've sadly had customers that have had oversubscription issues at different times of the day on different Blades and ASICs e.g. nightly backups etc. One customer had a six month problem with their Oracle backups and when we deployed the VirtualWisdom software we found that this was due to the oversubscription. Every other night the backups were causing the Blades to momentarily have link resets which in turn would reset each of their tape drives causing 'shoe-shining' and the prolonged backups. There was no way we could have identified this without the historically trending feature unless we physically saw this happen on the switches at the exact moment it occurred.
This is just one of many examples of problems that occur due to incorrect oversubscription.
Anyhow enough of the anecdotes here's the video: