When your disk array has a 2TB cache :)

Is that even efficient? I imagine there's a point where the overhead to manage such a large cache becomes greater than the benefits it provides, but maybe I'm wrong..

Besides, as far as I understand, the main benefit of a cache/swap space/page file on the HDD is allowing your system to retrieve some previously-computed data stored in that cache. Retrieving that pre-computed data is much quicker than needing to recompute it every time. Also that cached data is collocated with related data so the disk spends less time seeking between reads.

It's nice to have a few GB of swap space, but 2TB is way to much imho because you still have to touch disk to get at it. All that pre-computed data won't be nearly large enough to fill those 2TB.

So it's overkill unless you're running some highly specialized software that could benefit from massive amounts of caching eg: storing the results of 100s of millions of different db queries assuming that writes to the db don't invalidate the cache, because there's a ton of overhead right there.

I'd much rather have a system with like 32 GB of RAM so that I can dedicate 16+ GB of memory to caching. That's where it could make a huge difference in speed. Read speeds for RAM is measured in nanoseconds, SSD in microseconds, and HDD in milliseconds.

sauce:
https://people.eecs.berkeley.edu/~r...

It basically allows I/O's to complete to the array almost instantly as far as the host computer is concerned.

The array runs RAID 5 so you (mostly) avoid the usual performance impact of RAID 5 writes.

So the host does an I/O - its probably in the array cache - the array completes the I/O to the host (quickly), then the array sorts out the cache to the RAID 5 disks 'later'.

Its an SSD cache on the front of a bunch of spinners by the way!

@rozzzly I think you're thinking more of an application type cache, in which case I agree with you!