Early
mainframe storage designs took the promise that disk storage, which was cheaper
than main memory, could be treated as an extended virtual memory to swap memory-pages.
To achieve the fast data access, the data paths (or channels) between storage
and processor were widened, the storage bus kept adjacent to the processor bus
for data/signal integrity while boosting the channel speeds. Server attached storage
architectures dominated the scene for several years from mainframe processor
channels to PC Server bus slot and adapters.
A general
purpose SAS server performed a variety of tasks concurrently from running
applications, manipulating databases, file/print serving, providing communications,
and checking data-integrity to many housekeeping functions.
Another limitation imposed by the SAS
architecture was that of limited distance imposed by the interface - the OEMI
wide parallel connections in mainframes and wide differential parallel SCSI
connections in servers were limiting the distance between computers and servers
to a few meters. This led to the creation of raised-floor data centers but
posed a severe constraint and limitation on interconnectivity in multi-site operations.
NAS –
Network Attached Storage
Network Attached Storage, compared
to server attached storage on the other hand is a dedicated file server
optimized to do just one function only and do it well - file serving. NAS is a
system independent, shareable storage that is connected directly to the network
and is accessible directly by any number of heterogeneous clients or other servers.
In NAS, you
can add storage at random without disrupting the network. When the storage was
on the server as in SAS, the administrator had to take down the system, install
or upgrade the drives and bring the system back up again. That created a lot of
unacceptable downtime. NAS is being installed increasingly now to mitigate the downtime
associated with SAS. NAS is making inroads into the marketplace at different
price, performance and size levels.
SAN –
Storage Area Network
A SAN
(Storage Area Network) is a dedicated high performance network to move data
between heterogeneous servers and storage resources. Being a separate dedicated
network it avoids any traffic conflict between clients and servers. A fiber-channel
based SAN combines the high-performance of an I/O channel (IOPS and bandwidth)
and the connectivity (distance) of a network.
Adopting SAN
technology through the use of Fiber Channel and hubs and switches allows high-speed
server to storage, storage-to-storage or server-to-server connectivity using a
separate network infrastructure mitigates problems associated with existing network
connectivity. SANs have also the potential to allow cable lengths up to 500 meters
today and unto 10 km in future so servers in different buildings can share external
storage devices.
By - Dilshan Hemawardhane
continue reading
