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Introduction to SAN and NAS Disaster recovery strategies
Imagine this scenario, the disk is the bottleneck on your database server. At
this time you are also investigating disaster recovery options. Storage Area Network
(SAN) would solve both problems by delivering fibre optic speed
and a separate secure storage for your data. Incidentally, you often need
2 or 3 reasons before you embrace any new technology.
SAN and NAS could be deployed separately, but working together, SAN provides
fast scaleable storage while NAS provides clustering gives file level access to
the data. More and more, SAN and NAS will be thought of as an inseparable
pair, like 'TCP/IP'.
SAN and NAS Disaster Recovery Topics
DAS is an acronym that has been invented to describe a hard drive.
I just mention this way of thinking of your discs because it provides a baseline
for performance when you look at alternative storage devices like NAS and SAN.
Because departments are better at collecting information,
there is increasing pressure on the administrator to maintain a fast network,
while keeping the data secure. SAN is a great answer to data management overload.
 The SAN disk storage subsystem connects to the server through a Fibre
Channel. This channel has a HBA (Host Bus Adapter) on the server connecting fibre-optic
cables to the switching device, and finally on to the storage area.
Conceptually, a SAN is a separate arrat of storage devices. Think of
a SAN as a separate back-end network which is dedicated to data storage.
The advantages of SAN is that you can make server-less backup. This not
only removes the load from the server, but also eliminates
network traffic during backup.
 I once asked a professor of
Botany the best way of growing tomato seeds, he said, 'Guy read the packet,
it's in the gardener's interest to give you the very best information on growing
their seeds right there on the packet'. The relevance here is, if you want to know the technical
specification for SAN, then who better to contact than the manufacturers.
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Think of NAS as your gateway to the SAN. The NAS devices
bring an extra level of fault tolerance to the network. With hard disks, if the
server is down then data cannot be accessed by the clients, but with NAS, the data is still available on the network and accessible
by clients. You can also use RAID tactics with NAS and so ensure that the NAS device
is not a single point of failure.
NAS (Network Attached Storage) is a data storage mechanism that uses devices connected directly to the network media.
Each device has its own
IP address and is connected to the server which acts as a gateway to the data.
The advantage of NAS structure is that it means that you can have different
operating systems connected to a
centralised storage area. Another plus is the improved management, backup
and physical security of your data. One simple example of NAS is a CD-ROM
'jukebox' that are connected directly to the network.
These are the two mechanisms for connecting the server to the data stores.
Fibre Channel as expected uses Fibre optic and is serial in nature. SCSI
uses ethernet and is parallel in operation. The situation is that Fibre
Channel is expected to replace SCSI because of its speed and scalability.
Fibre Channel has its own switches and protocol and uses the HBA (Host Bus
Adapter) as a replacement for the SCSI adapter. SCSI is not giving up the
battle and you may see iSCSI a faster internet version.
Storage subsystems have an IP address on their I/O bus (SCSI ID or HBA).
Inside the storage system will be arrays of disks. Areas on these disks are accessed buy their LUN
(Logical Unit Number). LUN security
is a feature of the storage subsystem, which limits access to HBAs. Access to a
given LUN is granted based on the WorldWide Name (WWN) of the Host Based Adapter
(HBA).
A server device name is bound to a LUN through a specific HBA and eight-byte
storage port WWN. Each server HBA is explicitly bound to a storage volume
or LUN and access is explicitly authorized.
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