SAN BASICS

Storage Fundamentals Challenges in data storage and data management Storage Issues and evaluation of network storage. DAS NAS and SAN Protocols and Interfaces IP SAN Challenges in data storage and data management Data Active Data:  Product data: inventory, description, pricing, availability, sales numbers and projections  Customer data: orders, shipping details  Account data: banking, financial services industry  Medical data: health care providers, insurance industry, hospitals Information:  Buying habits and patterns of customers  Health history of patients  Locations where a credit card is used  Calls log for old mobile numbers Storage Issues and Evolution of Storage In the Enterprise-level storage technology, a few of the challenges faced are   Access:  Keeping data on-line and accessible for 24 hours a day. Movement: Ensuring data mobility and data sharing.  Growth:  Increasing volume of data drives need for  ever-increasing quantities of storage.Non-disruptively growing the number of applications, users, data, and infrastructure.  Management:  Establishing a single point from which to manage growing complexity and heterogeneity Security:  Ensure data access with security. Evaluation of Storage Management: Host Centric: In such systems, storage is directly connected by a dedicated channel to the server it supports. The amount of disk storage attached to such system has increased exponentially. Client- Server Environment: Distributed clients and servers run specific application needs and may therefore run different operating systems( such as windows NT, Unix, Novell Netware, VMS and so on.). Consequently they have different file systems and different data formats. Managing this multi-platform, multi-vendor, networked environment has become increasingly complex and costly.Multiple vendor’s software tools, and appropriately skilled human resources must be maintained to handle data and storage resource management on the many different systems in the enterprise. Network Computing: Since the distributed model of storage do not meet the needs of e-business enterprise, an improved way to increase efficiency and meet business requirements would be to  centralise storage and have it connected to  servers via a dedicated network. This eventually reduces the cost of managing the storage. Core Elements in Data Center Infrastructure Applications Databases – Database Management System (DBMS) Servers/Operating systems Networks (LAN and SAN) Storage arrays Data Center Infrastructure A customer order is entered via the Application User Interface on a Client The client access es the server over a Local Area Network A DBMS uses the operating system on the server to read and write this data to the physical location on a disk A dedicated Storage Area Network provides the communication link between the server and the storage array, and transports the read/write commands and data between the server and the storage Array A storage array receives the read/write commands and data from the server and performs the necessary operations to store the data on the physical disks Intelligent storage arrays can deliver the requested data within a few milliseconds, and are typically configured to protect data in the event of drive failures

SAN: Storage Area Networks

A SAN is a dedicated network that is separate from LANs and WANs. It is generally used to connect all the storage resources connected to various servers. It consists of a collection of SAN Hardware and SAN software. The hardware typically has high inter-connection rates between the various storage devices and the software manages monitors and configures the SAN.  Types Of Storage Topologies SAN DAS NAS

SAN (Storage Area Network) Protocols

Storage Area Networks are traditionally connected over Fibre Channel networks. Storage Area Networks have also been built using SCSI (Small Computer System Interface) technology. An Ethernet network which was dedicated solely to storage purposes would also quality as a SAN.

Internet Small Computer Systems Interface (iSCSI) is a SCSI variant which encapsulates SCSI data in TCP packets and transits them over IP networks.

Fibre Channel over TCP/IP (FCIP) tunnels Fibre Channel over IP-based networks.

The Internet Fibre Channel Protocol (iFCP) transports Fibre Channel Layer 4 FCP on IP networks.  Storage is accessed at a block-level via SCSI Any to Any connectivity Cache is Implemented between the server and cache High performance interconnect Interoperability Complex management

Advantages of SAN

By integrating storage devices, SAN increases the storage space usability and cost efficiency.

SAN is the high-speed storage sharing system
SAN increases the network bandwidth and reliability of data I/O.
SAN is separated from the regular network system, and has an ability to expand the storage capacity.
SAN reduces the cost of the storage management since it simplifies the system fabric and devices management.
High bandwidth Fibre Channel
SCSI extension Block I/O
Resource Consolidation Centralized storage and management
Scalability Up to 16 million devices
Secure Access Isolation and filtering

Protocols 

iSCSI: Internet Small Computer System Interface

Internet Small Computer System Interface (iSCSI) is a TCP/IP-based protocol for establishing and managing
connections between IP-based storage devices, hosts and clients, which is called Storage Area Network (SAN). The
SAN makes possible to use the SCSI protocol in network infrastructures for high-speed data transfer at the block
level between multiple elements of data storage networks. 

SCSI: Small Computer System Interface

Small Computer System Interface (SCSI), an ANSI standard, is a parallel interface standard used by Apple
Macintosh computers, PCs, and many UNIX systems for attaching peripheral devices to computers. SCSI interfaces
provide for faster data transmission rates than standard serial and parallel ports. In addition, you can attach many
devices to a single SCSI port. There are many variations of SCSI: SCSI-1, SCSI-2, SCSI-3 and the recently
approved standard Serial Attached SCSI (SAS). 

SCSI-1 

SCSI-1 is the original SCSI and it is obsolete so far. Basically, SCSI-1 uses an 8-bit bus, and supports data rates of 4
MBps.

SCSI-2 

SCSI-2 is an improved version of SCSI-1. SCSI-2 is based on CCS which is a minimum set of 18 basic commands
all manufacture's hardware would work together. SCSI-2 also provided extra speed with options called Fast SCSI
and a 16-bit version called Wide SCSI. A feature called command queuing gave the SCSI device the ability to
execute command in an order that would be most efficient. Fast SCSI delivers a 10 MB/sec transfer rate. When
combined with the 16-bit bus, this doubles to 20 MB/sec. This is called Fast-Wide SCSI. 

SCSI-3 

SCSI-3 has many advances over SCSI-2 such as Serial SCSI. This feature will allow data transfer up to 100MB/sec
through a six-conductor coaxial cable. SCSI-3 solves many of the termination and delay problems of older SCSI
versions. SCSI-3 eases SCSI installation woes by being more plug-and-play in nature, such as automatic SCSI ID
assigning and termination. SCSI-3 also supports 32 devices while SCSI-2 supports only 8.   
FC & FCP: Fibre Channel and Fibre Channel Protocol  
The Fibre Channel Standards (FCS) defines a high-speed data transfer mechanism that can be used to connect
workstations, mainframes, supercomputers, storage devices and displays. FCS addresses the need for very fast
transfers of large volumes of information and could relieve system manufacturers from the burden of supporting the
variety of channels and networks currently in place, as it provides one standard for networking, storage and data
transfer. Fibre Channel Protocol (FCP) is the interface protocol of SCSI on the Fibre Channel. 
Performance from 266 megabits/second to over four gigabits/second Support both optical and electrical media, working from 133 Megabits/sec up to 1062 Megabits/sec with
distances up to 10 km. 

Fibre Channel consists of the following layers: 

FC-0 -- The interface to the physical media 

FC-1 -- The encoding and decoding of data and out-of-band physical link control information for
transmission over the physical media 

FC-2 -- The transfer of frames, sequences and Exchanges comprising protocol information units. 

FC-3 -- Common Services required for advanced features such as striping, hunt group and multicast. 

FC-4 -- Application interfaces that can execute over fibre channel such as the fibre channel protocol for
SCSI (FCP). 

The fundamental entity in fibre channel is the fibre channel network. Unlike a layered network architecture, a fibre
channel network is largely specified by functional elements and the interfaces bet ween them. These consis t, in part,
of the following: 

N_PORTs -- The end points for fibre channel traffic. 

FC Devices -- The fibre channel devices to which the N_PORTs provide access. 

Fabric Ports -- The interfaces within a fibre channel network that provide attachment for an N_PORT.  
The network infrastructure for carrying frame traffic bet ween N_PORTs. 
Within a switched or mixed fabric, a set of auxiliary servers, including a name server for device discovery
and network address resolution. 

The principal fibre channel network topologies consist of the following: 

Arbitrated Loop -- A series of N_PORTs connected together in daisy-chain fashion.  

Switched Fabric -- A network consisting of switching elements. 

Mixed Fabric -- A network consisting of switches and "fabric-attached" loops. A loop-attached N_PORT
(NL_PORT) is connected to the loop through an L_PORT and accesses the fabric by way of an FL_PORT. 

FCIP: Fibre Channel Over TCP/IP 

Fibre Channel Over TCP/IP (FCIP) describes mechanisms that allow the interconnection of i slands of Fibre Channel
storage area networks over IP-based networks to form a unified storage area network in a single Fibre Channel
fabric. FCIP relies on IP-based network services to provide the connectivity between the storage area network
islands over local area networks, metropolitan area networks, or wide area networks. 

iFCP: Internet Fibre Channel Protocol

Internet Fibre Channel Protocol (iFCP) is a gateway-to-gateway protocol, which provides fibre channel fabric
services to fibre channel devices over a TCP/IP network. iFCP uses TCP to provide congestion control, error
detection and recovery. iFCP's primary objective is to allow interconnection and networking of existing fibre
channel devices at wire speeds over an IP network. The protocol and method of frame address translation defined
permit the attachment of fibre channel storage devices to an IP-based fabric by means of transparent gateways. 

 FIBRE CHANNEL TOPOLOGIES

POINT TO POINT

FC - AL

SWITCHED FABRIC

POINT TO POINT

This is the simplest topology of the FC SAN, which allows the host and storage to connect directly. With point-to- point topology, the pro is transmitting speed is high, but the con is the limitation of the system expansion. Hence, several HBA cards are involved to connect from the server to storage devices in order to make the system expansion.

FC-AL (Fibre Channel –Arbitrated Loop)

All devices are connected  serially in a loop or ring, similar to token ring networking.
Every device has Transmitter and Receiver
Only two devices can communicate at a time, rest are blocked. This is called blocking technology
The failure of one device causes a break in the ring.
Fibre Channel hubs exist to connect multiple devices together.
THE FC-AL follows 8 bit pattern of Addressing called AL-PA
Only 127 are supported as the rest are affected by  ‘+’ and ‘-’ volts
Address 00 has the highest priority and reserved for FL port

SWITCHED FABRIC

Network consisting of Switching elements maximum of 239 switches per Fabric
1 – 239 switches can be placed in a fabric
Every switch is identified by a domain number, and up to 239 domains are available in a fabric.
The addressing pattern followed in a switch is 24 bit addressing called  PID (Port Identifier)
Up to 16 million devices can be connected to the fabric
Practically 16000 devices are connected with in a fabric.

DAS DIRECT ATTACHED STORAGE

Direct-attached storage (DAS) is computer storage that is directly attached to one computer or
server and is not, without special support, directly accessible to other ones. The main alternatives to direct-attached storage are network-attached storage (NAS) and the storage area network (SAN). 
 
For an individual computer user, the hard drive is the usual form of direct-attached storage. In an
enterprise, providing for storage that can be shared by multiple computers and their users tends to be more efficient and easier to manage. 

Storage is captive ‘behind’ the server, limited mobility
Point to point connectivity
Block I/O
Limited scalability due to limited devices                        
No efficient storage sharing possible
Costly to scale and complex to manage
The main protocols used for DAS connections are ATA, SATA, SCSI, SAS and Fibre Channel.

DAS Challenges

 Hosts must be directly connected
 Scalability is limited
 Number of connectivity ports to hosts
 Number of addressable disks
 Distance limitations
 Downtime required for maintenance

NAS NETWORK ATTACHED STORAGE

NAS is file-level computer data storage connected to a computer network providing data access to
heterogeneous clients. As of 2010 NAS devices are gaining popularity, as a convenient method of sharing files among multiple computers.Potential benefits of network-attached storage, compared to file servers, include faster data access, easier administration, and simple configuration.

NAS Features 

Any to any connectivity
File I/O
Storage is accessed at a file level via NFS or CIFS
Storage is accessed over an IP network
Storage devices can be shared between servers
Files can be shared between users

NAS Challenges

Speed
Reliability
Connectivity
Scalability

Speed

Network latency and congestion
Protocol stack inefficiency encapsulation, possessor overhead, and relatively small payload
Application response requirements

Reliability

Due to the large geographical coverage of enterprise networks there are inherent possibilities
for network failures, but with redundancy planning these issues can be minimized.
Centralized storage silos may become single points of failure without remote mirroring or
backup facilities.

Connectivity

Without newly emerging technologies, iSCSI, FCIP & iFCP, many applications required block
level access therefore excluding NAS as a solution for businesses

Scalability

Although NAS devices can scale to terabytes of storage capacity, once the capacity isexhausted the only way to expand is to add additional devices. This can cause additional
problems when data center real estate is at a premium
Once a NAS device is fully populated, including external storage enclosures, the onlyremaining scaling option is to buy another system. When data center real estate is at a
premium this can be seen as a major limitation.