Instead of looking at fmserver.exe through the OS performance tools, make sure your FMS is set up to collect usage statistics logs (it's off by default). With that on then look at the various counters FMS collects and see if you can detect where it spends its time. The counters cover the 4 traditional bottlenecks: memory, processing, disk i/o and network throughput.
I highly suspect that your usage of iSCSI may be an issue. SAN is largely ok but when using dedicated fibrechannel, not iSCSI.
Is this a virtual box? Can you assign it a hard disk that is internal?
You did not state if you were on wifi or 3G/4G/4G which can make a big difference nor did you state the size of the file you were displaying. I would have a lower quality image to display on mobile device especially if you are using 3g. I have FMS13 running on a windows 8 pro machine, 8Gb Ram, standard 7200RPM harddrive. I store hi-res images from an iPhone, the images are store and retrieved to display and both functions work well using wifi. I have not tested using 3g/4g/LTE.
iSCSI running through built-in ethernet 'screams' bottleneck, but iSCSI running through quad 10Gig Ethernet ports is far less expensive than Fibre Channel and much faster. Also he mentions iSCSI, but no mention of the drive system behind it. iSCSI running a small set of spinning disks with RAID-6 is going to be much slower than a larger set of SSDs running RAID-10 with a quality, active-active filer head.
As the 'unofficial' defender of cloud architecture and virtualization- I have to agree with Wim that the shared iSCSI disk is suspect in this example, but I had to point out that there are ways to 'do it right' and have superior performance. i also have to point out that shared storage is often a key component in load balancing and fault tolerance in a virtualized environment.
The implication in the response is that shared storage may be inferior to a local disk; however, when applied cautiously the use of iSCSI can create a system with no single point of failure- something that most FileMaker Server architectures can not claim.
I concur with Wim's post; however, I just had to stick up for the 'virtual' guys...
I agree with Win's post too. I was pointing out some additional factors.