Exchange 2013 database corruption with event 476 in ESE

There a lot of determining factors that go into the performance feeling here. One tweak you might consider is setting up Jumbo Frames. Scott Lowe has a recent blog post here that shows some of what he did to achieve this.

You mention that the guests will be running low CPU load - those are always great candidates for virtualization - but the difference between FiberChannel and iSCSI doesn't really come into play yet.

If your vm guests are going to be running storage-intensive operations, then you have to consider that the speed of transferring a read/write operation from the VM Host to the storage array may become your bottleneck.

Since your typical iSCSI transfer rate is 1Gbps (over Ethernet), and FC is usually around 2-4Gbps (depending on how much cash you're willing to spend), then you could state that the transfer speed of FC is roughly twice as fast.

There's also the new 10Gig-E switches, but your Powervault and Powerconnect don't support that yet.

However, that doesn't really mean that the machines will work faster, as if they are running applications with low I/O, they might actually perform at the same speeds.

The debate as to which is better is never ending, and it basically will depend on your own evaluation and results.

We have multiple deployments of FC-based mini-clouds and iSCSI-based mini-clouds, and they both work pretty well. We're finding that the bottleneck is at the storage array level, not iSCSI traffic over 1Gb Ethernet.

The key to a good VMWare storage platform is understanding what kind of load VMWare generates.

• First, since you host a lot of servers, the workload is typically random. There are many IO streams going at the same time, and not many of them can be successfully pre-cached.
• Second, it's variable. During normal operations, you may see 70% random reads, however the instant you decide to move a VM to a new datastore or something, you'll see a massive 60GB sequential write. If you're not careful about architecture, this can cripple your storage's ability to handle normal IO.
• Third, a small portion of your environment will usually generate a large portion of the storage workload.

The best way to approach building storage for a VMWare platform is to start with the fundamentals.

• You need the ability to service a large random read workload, which means smaller faster drives, as well as possibly SSD. Most modern storage systems allow you to move data around automatically depending on how it's accessed. If you are going to use SSD, you want to ensure this is how you use it. It should be there as a way of gradually reducing hot-spots. Whether you use SSD or not, it's beneficial to be able to put all the work across all the drives, so something with a type of storage pooling would be beneficial.
• You need the ability to service intermittent large writes, which doesn't care as much about the spindle speed of the underlying drives, but does care about the controller stack's efficiency and the size of the cache. If you have mirrored caching (which is not optional unless you're willing to go back to backups whenever you have a controller failure), the bandwidth between the two caches used for mirroring will be your bottleneck for large sequential writes, usually. Ensure that whatever you get has a high speed controller (or cluster) interconnect for write caching. Do your best to get a high speed front end network with as many ports as you can get while remaining realistic on price. The key to good front end performance is to put your storage load across as many front end resources as possible.
• You can seriously reduce costs by having a tier for low priority storage, as well as thin provisioning. If your system isn't automatically migrating individual blocks to cheap large/slow drives (like nearline SAS or SATA with 7200 RPM and 2TB+ sizes), try to do it manually. Large slow drives are excellent targets for archives, backups, some file systems, and even servers with low usage.
• Insist that the storage is VAAI integrated so that VMWare can de-allocate unused parts of the VMs as well as the datastores.