Ai... Sick of their promises
We have been struggling with their product for the past 3 years - and twice upgraded controllers just to resolve issues with the system. Currently running the 6.2 release. We bought into the SSD tiering KoolAid, only to find out it does not really work. Data progression only runs once a day, so when the tier fills up, all writes go to disk. <SPLAT> goes performance. When data progression runs, it does not move all of today's writes down to the next tier, so a bigger SSD tier is needed to cover that. But then if you don't have enough in tier3, then tier2 does not work right.
Then there is another issue we continually battle. When a disk fails, most SANs just mark it as bad, restripe to a new disk and go. Not compellent. they try to keep a flaky disk running as long as possible. So when it starts burping, the performance of the entire array stalls until the disk settles down. In the logs you can sometimes see which disk is having a problem... Then when it comes time to replace a disk, it takes about a day for the SAN to release it. It moves data off the bad disk onto the hot spare... yes, I typed that correctly. So when the bad disk burps as it is now being attacked intensely to move data off of it, the SAN can freeze up again.
Of course, we are running over 500 VMs against this SAN, so when it stalls, bad things happen. One of the side effects is that the iSCSI stack on ESXi gets locked up, bringing the hypervisor to a standstill. 80% of the time we can get out safely - that is with performance similar to a newbie trying to learn to drive a car with a manual transmission. Takes about 2 hours until the jerking stops. 20% of the time, ESXi locks up so bad we have to start rebooting hosts... and writing letters to our customers. Joy.