software defined storage is looking to be as confusing as SDN
the whole SDN space is a mess, even one of the early founders of the concept said as much.
SDS is looking to be just as bad, if not worse. At least with networking for the most part it is stateless. If a switch goes down, or a router goes out, you may(or may not) have some downtime but the amount of risk involved(IMO) is significantly less than if say your storage resource becomes unavailable!
It's important to keep things simple enough to manage and troubleshoot. I'm (thus far) not a fan of grid storage for transactional applications, I'm sure it's fine for object storage/archival etc. Too much risk for transactional. The software has to be really complicated.
Storage is often striped over a large amount of resources (networking significantly less so), and so you're obviously only as strong as the weakest link. A few years ago in a more traditional enterprise class storage array I had an incident where roughly 9/300 disk drives were operating at a drive temperature that was too low (19C). While the official operating specs of the drives listed operating temps WELL BELOW 19C, they did not say the firmware had hard coded instructions to exponentially slow down the drive heads the colder the drive got.
As a result these drives were returning 300-500ms response times. For volumes that are striped across every drive in the system(all of them) this naturally caused some problems. Most other drives were in the 20-30ms range and these were 10x that. It took some time to troubleshoot, at first I thought it was just bad drives so we tried replacing one of them to no avail. They got in contact with the manufacturer of the drive in question and they confirmed the behavior, and so the only short term course of action was to increase the temp. Fortunately the array was in somewhat of a private suite in the data center so we could increase the ambient temp in the room by about 3-4 degrees F which addressed the problem (along with closing off some cold air vents near the array). This allowed all drives to remain at 20C or above and the problem stopped. Fortunately the effects were not crippling, but they were noticeable. I believe the thermostat was set to 68 or 69 in the DC. Though the array sat upon a big steel plate which was ice cold, which may of contributed to a lower temp in the area around the array.
I don't know about others but I never considered 19C to be "too cold", if anything I would expect significantly colder to be too cold.. but it was an interesting experience anyway.