HA: A3500 vs. FC/AL

[Seth Rothenberg]

The A3500 has a controller and a cache.
The A5200 (I have been told) has no controller or cache.
There are many Host-based cache products available.
None of them is appropriate for our application, which
does synchronous writes.

Our application receives data from an external source, 
writes the data to disk, does a flush, then acknowledges receipt
or data from the external.  If the write were only as far as 
the host-based controller, a failover then would not
guarantee that the latest data is available to the 
secondary host.

Host-base Write Cache is not appropriate for our application.
Your Mileage may vary.

We actually look forward to using Solaris' disk read cache, 
which means that recently-written pages are still in memory.
Thus, Queue I/O can occur with fewer reads from disk.
(We currently see 80% hits.  With 6 times as much memory,
I hope the new system will have closer to 95%.)
I have recently bought books on tuning for just this reason....

Seth