NAS was pretty much a necessity back in the era of desktops and individual servers. You could mount people's home directories on a CIFS or NFS share (depending on their OS). People could share their files with each other by simply copying them to a shared directory. You saw block storage devices being exported to these desktops via iSCSI sometimes, but usually block storage devices were attached to physical servers in the back room on dedicated storage networks that were much faster than floor networks. The floor networks were fast enough to carry CIFS, but CIFS at its core is just putting and getting objects, not blocks, and can operate much more asynchronously than a block device and thus wasn't killed by latency the way iSCSI is.
But there's problems too. For one thing, every single device has to be part of a single login realm or domain of some sort, because that's how you secure connections to the NAS. Furthermore, people have to be put into groups, and access set on portions of the overall NAS cloud based on what groups a person belongs to. That was difficult enough in the days when you just had to worry about Linux servers and Windows desktops. But now you have all these devices
Which brings up the second issue with NAS -- it simply doesn't fit into a device-oriented world. Devices typically operate in a cloud world. They know how to push and pull objects via http, but they don't speak CIFS or NFS, and never will. What we are seeing is that increasingly we are operating in a world that isn't file based, it's object based. When you go into Google Docs to edit a spreadsheet, you aren't reading and writing a file. You're reading and writing an object. When you are running an internal business application, you are no longer loading a physical program and reading and writing files. You're going to a URL for a web app that most likely is talking to a back end database of some kind to load and store objects.
Now, finally, add in what has happened in the server room. You'll still see the big physical iron for things like database servers. But by and large the remainder of the server room has gone away, replaced by a private cloud, or pushed into a public cloud like Amazon's cloud. Now when people want to put up a server to run some service they don't call IT and work up a budget and wait months for an actual server to be procured etc., they work at the speed of the cloud -- they spin up a virtual machine, they attach block storage to it for the base image and for any database they need beyond object storage, and they implement whatever app they need to implement.
What this means is that block storage and object storage integrated with cloud management systems like OpenStack are the future of enterprise storage, a future that alas did not arrive soon enough for the vendors of scale-out block storage that survived the previous decade, who ended up without enough capital to enter this brave new world. NAS won't go away entirely, but it will increasingly be a departmental thing feeding desktops on the floor, not something that anything in the server room uses. And that is, in fact, what you see happening in the marketplace today. You see traditional Big Iron vendors like HDS increasingly pushing object storage, and the new solid-state storage vendors such as Pure Storage and Solidfire are predominantly block storage vendors selling into cloud environments.
So what does the future hold? For one thing, lower latencies via hypervisor integration. Exporting a share via iSCSI then mounting it via the hypervisor has all of the usual latency issues of iSCSI. Even with 10 gigabit networking now hitting affordability and 25 to 100 gigabit Ethernet in the future, latency is a killer if you're expecting a full round trip. What if writes were cached on a local SSD array, in order, and applied in order? For 99% of the applications out there this provides all the write consistency that you need. The cache will have to be turned off prior to migrating the virtual machine to a different box, of course -- thus the need for hypervisor integration -- but other than a catastrophic failure (where the virtual machine will go lights out also and thus not have inconsistent data when it is restarted on another node) you will, at best, have some minor data loss -- much better than inconsistent data.
So: Block storage with hypervisor and cloud management integration, and object storage. The question then becomes: Is there a place for the traditional dedicated storage device (or cluster of devices) in this brave new world? Maybe I'll talk about that next, because it's an interesting question, with issues of data density, storage usage, power consumption, and then what about that new buzzword, "software defined storage"? Is storage really going to be a commodity in the future where everybody's machine room has a bunch of generic server boxes loaded with someone's software? And what impact, exactly, is solid state storage having? Interesting things to think about there...