IBM TotalStorage DS300 Best Practices Manual page 38

by default, is configured to run with File System I/O. It cannot utilize a "raw I/O" to
achieve improved performance.
Application server directs
file I/O request over the
LAN to remote file system
in the NAS appliance
Figure 2-5 NAS uses file I/O
NAS offers a number of benefits, which address some of the limitations of directly
attached storage devices and overcome some of the complexities associated
with SANs.
Resource pooling: An NAS appliance enables disk storage capacity to be
consolidated and pooled on a shared network resource, at great distance
from the clients and servers which will share it. Therefore, an NAS device can
be configured as one or more file systems, each residing on specified disk
volumes. All users accessing the same file system are assigned space within
it on demand. This contrasts with individual DAS storage, when some users
may have too little storage, and others may have too much. Consolidation of
files onto a centralized NAS device can minimize the need to have multiple
copies of files spread across distributed clients. Therefore, overall hardware
costs can be reduced. NAS pooling can reduce the need physically to
reassign capacity among users. The results can be lower overall costs
through better utilization of the storage, lower management costs, increased
flexibility, and increased control.
Exploits existing infrastructure: Because NAS utilizes the existing LAN
infrastructure, there are minimal costs of implementation. Introducing a new
network infrastructure, such as a Fibre Channel SAN, can incur significant
hardware costs. In addition new skills must be acquired, and a project of any
size will need careful planning and monitoring to bring to completion.
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IBM TotalStorage DS300 and DS400 Best Practices Guide
Application
server
IP network
File I/O
IP protocol
NAS Appliance
File system in NAS
appliance initiates block
I/O to NAS integrated disk