For those that live, breath, and eat storage (like me), this white paper that you can download below really sums it up well. Frankly, the advantage in data tiering performance as compared to the number of storage companies providing a "Cache" of your hot data is staggering.
Cache can fill up...especially with larger data sets. When this cache gets full, the only thing that the SAN can do is downgrade to writing and/or reading on the lower tier disks. Internally at Cyber Advisors, we call this a Cache Crash. It's not pretty.
Looking at our storage practice, we prefer the tiering of data that Dell Compellent provides. Cache Crashes can't and don't happen. Data is moved safely from one tier to the other based on algorithms of hot -vs- cold data. Measurements and continuous monitoring takes place to determine if any of your tiers is getting full, and disk can be added to any tier on the fly. It's safer.
To review this white paper, please click the button below: