iSCSI, NFS, FC or FCoE – Which is best for VMware?

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This has been a hot topic for many years, but in my opinion, the answer is very simple. It is easily explained by the fact that most enterprises deploy EMC VMAX and VPLEX, and HDS VSP storage platforms.

VSP only supports FC and FCoE, VPLEX only FC (the recently announced vVPLEX solution does support iSCSI, but this is specifically targeted at the SMEs) and VMAX supports FC, FCoE and iSCSI, but I believe iSCSI is rarely used.

So what could be the reason? Let’s take a quick look at each of the protocols:

iSCSI has one major thing going for it – low cost, but it does have a couple of drawbacks:

  • As standard Ethernet is not lossless under high load, it can become unreliable
  • To guarantee packet delivery, TCP is used, but since this was not designed for storage, it adds an overhead

NFS has the same benefits and limitations as iSCSI, but adds a couple of other issues to the list:

  • NFS v3 lacks the ability to utilize multiple sessions and paths from the host to a datastore – this affects performance and reliability (this would be addressed if VMware were to adopt NFS v4.1/pNFS)
  • The time taken for planned and unplanned fail-overs is significantly greater for block protocols. This requires timeout settings to be increased on both the hypervisor and guest VMs (i.e. to 120 seconds)
  • Some Microsoft applications are not compatible with NFS (Microsoft Cluster Service and Exchange for example)

FC and FCoE
Fibre Channel has been the dominant high-end storage protocol for many years. It is lossless and was designed from the ground up to deliver high performance (with speeds up to 16 Gbs) and to be a reliable storage connectivity solution.

However, it is now being forced to evolve by Fibre Channel over Ethernet because:

  • Ethernet has an aggressive road-map to deliver 40 Gbs and 100 Gbs
  • Converged Network Adapters (CNAs) provide both a storage and LAN adapter to a host, thus significantly reducing cabling and switch port requirements
  • FCoE is fully interoperable with existing Fibre Channel devices (i.e. CNAs can be used to connect to FC arrays using TOR switches that support both FC and FCoE)

So if you want the best performing and reliable storage protocol, then you have to be looking at FC or FCoE., If you are going to deploy 10 GbE then it makes sense to consider CNAs and FCoE.

If your requirements and budget are more modest then iSCSI or NFS, using GbE would prove to be an excellent choice and will return great value for money.

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