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:
