The run up to Christmas (or Autumn term if you prefer) is always our busiest time of year as measured by the number of searches performed by our users. Last year the search response times were not what we would have liked and we have been investigating the causes of the poor performance and ways of improving it. Our IT people determined that at our busiest times the disk drives in our SAN were being pushed to their maximum performance and just couldn’t deliver data any faster. So, over the summer we have installed an array of Solid State Disks to act as a fast cache for our file-systems (for the more technical I believe it is actually configured as a ZFS Level 2 Cache.)
The SSD cache was turned on during our brief downtime on Thursday morning and so far the results look promising. I’m told the cache is still “warming up” and that performance may improve still further. The best performance indicator I can provide is the graph below. We run a “standard” query against the database every 30 minutes and record the time taken to run the query. The graph below plots the time (in seconds) to run the query since midnight on the 23rd August 2011. I think it is pretty obvious from looking at the graph exactly when the SSD cache was configured in.
It all looks very promising so far and I think we can look forward to the Autumn with less trepidation and hopefully some happier users.