HF40 what happens if you lose 1 drive on the cache tier

[jeff2000]

IS the entire cache tier gone? What is the level or RAID protection in the cache tier. Thank you.

[Sheldon Smith]

If a cache drive fails, that portion of the cache is lost.  It will have to read from the HDDs with some already-cached data getting kicked out a little earlier than usual.

Cache doesn't have or need RAID.

[jeff2000]

Thank you for the response. I must be a little confused as I am coming from a compellent shop. I had assume the cache tier was more like a persistent tier in other teiring arrays. How is hot data kept in cache or is it? It must be protected somehow, is it mirored between controllers? Thank you.

[Sheldon Smith]

Hot data stays in cache until it cools off enough and gets overwritten.

HFxx: Hybrid Flash. HDDs with SSD cache. Data is never stored in the SSDs. All volumes reside permanently in the HDDs. HDDs use Triple+ RAID, and as I wrote earlier, SSDs are just JBODs. If you need a larger cache, pull an SSD, put a larger one in. Give it time (a day?) to fully warm up, then replace the next SSD. It is possible to "pin" a volume in cache, so the volume never leaves cache but that's at the expense of the rest of the system's cache needs. And of course the volume must be small enough to completely fit.

Data is written to the system, mirrored in the two controllers' internal caches and written to the HDDs. As it starts to cool it moves out to the common SSD cache. A key thing to remember: The SSD cache is not protected. It doesn't need to be; it's just cache!
Reading involves checking the system's internal cache then the cache SSDs. If not found in the SSDs, then read back in from disk.

As opposed to the AFxx series: All Flash. SSDs store the data using Triple+ RAID with no need for SSD cache.

All this should be in the Administrative Guide. Somewhere.  8^)