NAS Concepts
NAS Architecture
Comparing Architectures
DAS
NAS
Host
ser
Application Application
U
File
NAS
Appliance
FS interface
I/
FS interface
O
Local File system FS protocol
Storage
OS
SCSI driver
B
l
TCP/IP
o
ck I
O
I/
HBA driver
/
O
File
NIC driver
a
re
w
HBA
NIC
a
rd
H
With NAS, file I/O is redirected over a network. File I/O means commands to
open and close files and read and write bytes of data from files. Contrast this
with local file storage or SAN, which is block-based I/O. With block-based I/O,
the host must tell the storage controller exactly what logical blocks to read or
write. With NAS, the host tells the NAS appliance what file to open. With NAS,
the block-to-file abstraction layer occurs in the NAS appliance instead of in the
host.
A driver in the client system interprets each file I/O request to determine if it
should be conveyed over the LAN. If so, it uses the underlying protocol stack
and system functions to transmit the file request over the LAN to a NAS
system, which performs the requested actions.