In most cases, a failing or bad hard disk should not cause any service disruption to the ProxySG or CacheFlow appliance. It is possible to take a hard disk offline as a precautionary measure.
Do not replace the hard disk without removing its power source unless your ProxySG supports hot-swapping of hard disks. For ProxySG models that support hot-swapping of hard disks, refer to https://support.symantec.com/en_US/article.TECH243318.html.
Cacheflow 5000 and 500 both support hot-swapping of hard disks.
Use the "disk offline" command.
offline Take a disk offline