Information Technology Reference
In-Depth Information
Working with NFS Datastores
NFS datastores are used in much the same way as VMFS datastores: as shared pools of storage
for VMs. Although VMFS and NFS are both shared pools of storage for VMs, they are different
in other ways. The two most important differences between VMFS and NFS datastores are as
follows:
With NFS datastores the i le system itself is not managed or controlled by the ESXi host;
rather, ESXi is using the NFS protocol via an NFS client to access a remote i le system man-
aged by the NFS server.
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With NFS datastores all the vSphere elements of high availability and performance scaling
design are not part of the storage stack but are part of the networking stack of the ESXi host.
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These differences create some unique challenges in properly architecting an NFS-based solu-
tion. This is not to say that NFS is in any way inferior to block-based storage protocols; rather,
the challenges that NFS presents are simply different challenges that many storage-savvy
vSphere administrators have probably not encountered before. Networking-savvy vSphere
administrators will be quite familiar with some of these behaviors, which center on the use of
link aggregation and its behavior with TCP sessions.
Before going into detail on how to create or remove an NFS datastore, we'd like to i rst
address some of the networking-related considerations.
Crafting a Highly Available NFS Design
High-availability design for NFS datastores is substantially different from that of block storage
devices. Block storage devices use MPIO, which is an end-to-end path model. For Ethernet net-
working and NFS, the domain of link selection is from one Ethernet MAC to another Ethernet
MAC, or one link hop. This is coni gured from the host to switch, from switch to host, and from
NFS server to switch and switch to NFS server; Figure 6.44 shows the comparison. In the i gure,
“link aggregation” refers to NIC teaming where multiple connections are bonded together for
greater aggregate throughput (with some caveats, as we'll explain in a moment).
Figure 6.44
NFS uses the net-
working stack, not
the storage stack,
for high availability
and load balancing.
MPIO Domain
Link
aggregation
domain
Link
aggregation
domain
Interface 1
Interface 1
Interface 2
Interface 2
Storage
object
Datastore
