@Pete-S said in Local Storage vs SAN ...:
vSAN is basically local storage from several hosts networked together and replicated. It provides shared storage for the hosts. DRBD, Gluster and Ceph are simply technologies used to build a vSAN.
Technically none of those are vSAN. vSAN is a specific means of providing RLS using traditional SAN stack tech. It came about later than RLS. These three all predate vSAN concepts. Starwind does vSAN, for example.
With a vSAN approach you either have something directly on the hypervisor or more commonly a virtualized SAN appliance on a VM. This approach is only common on VMware because it is so lacking in basic features that it is necessary there, just like it is the only platform that requires hardware RAID - everyone else has software RAID built in.
The upside to vSAN is that it "looks" just like SAN in every sense and vendors trying to push you to SAN are fooled because all they see are the iSCSI or ATAoE or whatever adapters in place.
Traditional RLS like CEPH, DRBD, etc. don't have the SAN protocol layer making them simpler, faster, and more robust. There is little value in putting them in a VM so they tend to be deployed in the hypervisor directly.
Some, like Gluster, require a local driver and show up as being Gluster at the driver level. Others, like DRBD, mount as a local filesystem and are undetectable at that level of abstraction and appear as if you are using a regular local disk. Any system trying to detect local disk would believe that that is what it had.
So while the new VMware world vSAN approach has gotten a lot of attention as a way to "replace SAN" using RLS, it's mostly marketing buzz. RLS techniques are old and have been around long before virtualized SAN was imagined as having value. DRBD wasn't the first in 2007, but it was an early player in the enterprise space. But RLS goes back to the 1970s long before SAN or VMware.
Also worth noting, most SAN is actually vSAN. vSAN doesn't imply that it runs on the same box or is RLS. It's a different layer of concept.
SAN refers to block storage over a networking encapsulation protocol and has a set of protocols known as the SAN protocols that are normally used (FC, iSCSI, etc.)
vSAN is any SAN run virtualized (which is how production workloads are generally run, so lots of SAN is done this way.) Most shops building their own SANs will build vSAN without even thinking about it. It's just SAN in a VM. Being in a VM means it COULD be local, could be distant, it's not specified.
Neither SAN or vSAN implies any redundancy, only that the storage is block and over a remote networking protocol and vSAN only then implies that the workload has been virtualized making it all but a useless term (we don't call servers vServers in other contexts.)
RLS refers to the block storage being local AND replicated between nodes. Good SAN deployments have to use RLS to make themselves reliable. This is what a proper 3PAR or Clariion deployment will do - they have multiple nodes and RLS replicates so that a full node can fail. Under the hood, RLS is the only mechanism for redundancy if it truly exists.
For SAN to be truly reliable, it needs RLS. vSAN being SAN, same thing. Lots of vSAN is chosen because it is the smarter way to do SAN, but it still needs RLS to have that value. Many vSAN products include RLS setup out of the box, making people confuse the two, but the concepts are different. Lots of vSAN deployments aren't redundant and lack RLS, some aren't even local.
Starwind, as an example, offers vSAN that is non-redundant and remote (just a traditional SAN but with good technology.) And they offer vSAN that is clustered and redundant, but still remote and just a SAN cluster. Or you can move the VMs onto the hosts that they are providing storage for and make it RLS. All three are as designed.
It's complicated because vendors like VMware use concept names, like vSAN, as product names and market them as meaning something unrelated to their terms.
So all that to say vSAN is definitely an option here, if it is an RLS architected vSAN. Or another way.... vSAN is a tool, RLS is a solution. When solutioning, vSAN is one component that could be used to achieve RLS.