Very slow harddisk performance
The write-through cache could be a performance hit. Every write to the cache must be written to the disk straight away. A write-back cache can wait for the optimal time to write the data to disk. Depending on the hardware, this may require an battery-backup (on the array controller), and some controllers disable write caching if the battery is absent or needs replacing. You may want to verify if the array cache is in fact enabled. Some controllers don't make this very obvious.