Storage Area Network

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					Storage Area
Network
          V M Gunda
                                                     Storage Area Network

Contents
1       What is SAN ........................................................................................................................................ 3
    1      Universal Storage: .......................................................................................................................... 3
    2      Direct Attach Storage..................................................................................................................... 4
    3      Network Attached Storage Network ............................................................................................ 5
    4      Storage Area Network ................................................................................................................... 7
2       What Makes SAN Best ...................................................................................................................... 9
3       SAN Software ................................................................................................................................... 10
4       SAN Software Architecture ............................................................................................................. 11
5       Applications for SAN ........................................................................................................................ 11
6       Storage Network Architecture ........................................................................................................ 13
7       Storage System ................................................................................................................................ 14




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1 What is SAN

   A storage area network (SAN) is any high-performance network whose primary
   purpose is to enable storage devices to communicate with computer systems
   and with each other.

      It doesn’t say that a SAN’s only purpose is communication between
       computers and storage. Many organizations operate perfectly viable SANs
       that carry occasional administrative and other application traffic.
      It doesn’t say that a SAN uses Fibre Channel or Ethernet or any other specific
       interconnect technology. A growing number of network technologies have
       architectural and physical properties that make them suitable for use in SANs.
      It doesn’t say what kind of storage devices are interconnected. Disk and tape
       drives, RAID subsystems, robotic libraries, and file servers are all being used
       productively in SAN environments today. One of the exciting aspects of SAN
       technology is that it is encouraging the development of new kinds
       of storage devices that provide new benefits to users. Some of these will
       undoubtedly fail in the market, but those that succeed will make lasting
       improvements in the way digital information is stored and processed.

   The beauty of SANs is that they connect a lot of storage devices to lot of servers
   and place in the administrator’s hands the choice of which server gets to access
   which storage devices. Storage Area Technology involves:

             Architecture
             Storage
             Networking
             Software

1 Universal Storage:
  The problem with universal client – Server storage is that, if application B wants
  to access the application A stored data then it is like you need copy the data from
  Application A storage to Application B storage. It not only makes cumbersome
  but it is like make duplication of data as well which is not good. Here comes to
  Storage area network (SAN)




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2 Direct Attach Storage

  Direct attached storage is the simplest and most commonly used storage model
  found in most standalone PCs, workstations and servers. A typical DAS
  configuration consists of a computer that is directly connected to one or several
  hard disk drives (HDDs) or disk arrays. Standard buses are used between the
  HDDs and the computers, such as SCSI, ATA, Serial-ATA (SATA), or Fibre
  Channel (FC). Some of the bus cabling definitions allow for multiple HDDs to be
  daisy chained together on each host bus adapter (HBA), host channel adapter, or
  integrated interface controller on the host computer.

  This is what direct Attach storage looks like




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   The software layers of a DAS system are illustrated in Figure 2. The directly
   attached storage disk system is managed by the client operating system.
   Software applications access data via file I/O system calls into the Operating
   System. The file I/O system calls are handled by the File System, which
   manages the directory data structure and mapping from files to disk blocks in an
   abstract logical disk space. The Volume Manager manages the block resources
   that are located in one or more physical disks in the Disk System and maps the
   accesses to the logical disk block space to the physical volume/cylinder/sector
   address. The Disk System Device Driver ties the Operating System to the Disk
   controller or Host Bus Adapter hardware that is responsible for the transfer of
   commands and data between the client computer and the disk system.

3 Network Attached Storage Network
  After seeing the consequences of binding storage to individual computers in the
  DAS model, the benefits of sharing storage resources over the network become
  obvious. NAS and SAN are two ways of sharing storage over the network. NAS
  is generally referred to as storage that is directly attached to a computer network
  (LAN) through network file system protocols such as NFS and CIFS.
  The difference between NAS and SAN is that NAS does “file-level I/O” while SAN
  does “blocklevel I/O” over the network. For practical reasons, the distinction

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between block level access and file level access is of little importance and can be
easily dismissed as implementation details.




Logically, the NAS storage system involves two types of devices: the client
computer systems, and the NAS devices.
There can be multiple instances of each type in a NAS network. The NAS
devices present storage resources onto the LAN network that are shared by the
client computer systems attached to the LAN. The client Application accesses
the virtual storage resource without knowledge of the whereabouts of the
resource. In the client system, the application File I/O access requests are
handled by the client Operating System in the form of systems calls, identical to
the systems calls that would be generated in a DAS system. The difference is in
how the systems calls are processed by the Operating System. The systems
calls are intercepted by an I/O redirector layer that determines if the accessed
data is part of the remote file system or the local attached file system. If the data
is part of the DAS system, the systems calls are handled by the local file system.
If the data is part of the remote file system, the file director passes the
commands onto the Network File System Protocol stack that maps the file
access system calls into command messages for accessing the remote file
servers in the form of NFS or CIFS messages. These remote file access
messages are then passed onto the TCP/IP protocol stack, which ensures
reliable transport of the message across the network. The NIC driver ties the
TCP/IP stack to the Traditional computer storage is defined by each server and

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   attached the storage device, Ethernet Network Interface card. The Ethernet NIC
   provides the physical interface and media access control function to the LAN network.

   In the NAS device, the Network Interface Card receives the Ethernet frames
   carrying the remote file access commands. The NIC driver presents the
   datagrams to the TCP/IP stack. The TCP/IP stack recovers the original NFS or
   CIFS messages sent by the client system. The NFS file access handler
   processes the remote file commands from the NFS/CIFS messages and maps
   the commands into file access system calls to file system of the NAS device. The
   NAS file system, the volume manager and disk system device driver operate in a
   similar way as the DAS file system, translating the file I/O commands into block
   I/O transfers between the Disk Controller/ HBA and the Disk System that is either
   part of the NAS device or attached to the NAS device externally. It is important to
   note that the Disk System can be one disk drive, a number of disk drives
   clustered together in a daisy-chain or a loop, an external storage system rack, or
   even the storage resources presented to a SAN network that is connected with
   the HBA of the NAS device. In all cases, the storage resources attached to the
   NAS device can be accessed via the HBA or Disk controller with block level I/O.

   There are several techniques for moving data between computers: backup, file
   transfer, and inter process communication, to name a few. But the real issue is
   that the information services organization has to acquire and manage the extra
   resources required both to copy data from Computer A to Computer B and
   to store it at both sites. There’s no business reason for this duplication of effort,
   other than that a computer needs data that was produced by another computer.

4 Storage Area Network
  You can see in the above picture, that all devices are connected to one storage
  line called Storage Area Network. All servers are connected to storage SAN, with
  this architecture any application any data from the storage devices which any of
  the application stored.




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                        Storage Area Network




Benefits of Storage Area Network:

   Reducing the cost of providing today’s information services or providing or
    enabling new services that contribute positively to overall enterprise goals.
   If all online storage is accessible by all computers, then no extra
    temporary storage is required to stage data that is produced by one computer
    and used by others. This can represent a substantial capital cost saving.
   Reduces total enterprise capital cost for information processing without
    diminishing the quality of service delivered as reusing of TapeDrive which is
    little bit expensive
   Administrative and operational savings in not having to implement and
    manage procedures for copying data from place to place. This can greatly
    reduce the cost of people—the one component cost of providing information
    services that doesn’t go down every year
   SAN         connectivity enables    the    grouping     of    computers       into
    cooperative clusters that can recover quickly from equipment or application
    failures and allow data processing to continue 24 hours a day, every day of
    the year.




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2 What Makes SAN Best

  Rule 1: When designing a SAN to access critical enterprise data, make sure the
  SAN is highly available (i.e., can survive failures of both components in it and
  components attached to it) and make sure it can grow well beyond anticipated
  peak performance needs without disruption.

  Rule 2: When evaluating SAN implementation options, once the basic capacity,
  availability, and performance requirements can be met, look for advanced
  functionality available in the chosen architecture and consider how it might be
  used to further reduce cost or enhance the information services delivered to
  users.

  Rule: 3 Hardware makes SANs possible; software makes SANs happen.




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  3 SAN Software

     System applications: These applications build upon the basic SAN properties
     to provide a functionally enhanced execution environment for business
     applications. System applications include

            clustering,
            data replication,
            direct data copy between devices and
            The utility functions that use it, and so forth.

     Management applications. These applications manage the inherently more
     complex distributed system environment created by the presence of SANs.

            Zoning, device discovery
            Allocation
            RAID subsystem configurations are examples of applications that fall into
             this category.

SAN Software Capability

        Sharing Tape Drives: Tape drives indeed a very expensive devices.What is to
         keep a computer from (accidentally) writing to a tape while another computer
         is doing a backup? For two or three computers, an administrator can
         personally schedule tape drive usage so that this doesn’t happen. Here we
         required the software take care of two or more application scheduling the
         writing to it.
        Sharing Online Storage Devices: These are in housed RAID Sub System is
         similar to sharing Tape Drives. Except that more of it goes on and
         requirements for configuration changes are more dynamic. A typical
         enterprise RAID subsystem makes the online storage capacity of one or
         more arrays of disks appear to be one or more very large, very fast, or very
         reliable disks.
             o Application Failover
             o Sharing Data
             o Direct Data Movement between Devices




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4 SAN Software Architecture

                                            SAN is essentially the same as the
                                            software architecture of a DAS system.
                                            The key difference here is that the disk
                                            controller driver is replaced by either the
                                            Fibre Channel protocol stack, or the
                                            iSCSI/TCP/IP stack that provides the
                                            transport function for block I/O commands
                                            to the remote disk system across the SAN
                                            network. Using Fibre Channel as an
                                            example, the block I/O SCSI commands
                                            are mapped into Fibre Channel frames at
                                            the FC-4 layer (FCP). The FC-2 and FC-1
                                            layer provides the signaling and physical
                                            transport of the frames via the HBA driver
                                            and the HBA hardware. As the abstraction
                                            of storage resources is provided at the
                                            block level, the applications that access
                                            data at the block level can work in a SAN
                                            environment just as they would in a DAS
                                            environment. This property is a key
                                            benefit of the SAN model over the NAS,
                                            as some high performance applications,
                                            such as database management systems,
                                            are designed to access data at the block
  level to improve their performance. Some database management systems even
  use proprietary file systems that are optimized for database applications. For
  such environments, it is difficult to use NAS as the storage solution because NAS
  provides only abstraction of network resources at the file system level for
  standard file systems that the Database Management System may not be
  compatible with. However, such applications have no difficulty migrating to a
  SAN model, where the proprietary file systems can live on top of the block level
  I/O supported by the SAN network. In the SAN storage model, the operating
  system views storage resources as SCSI devices. Therefore, the SAN
  infrastructure can directly replace Direct Attach Storage without significant
  change to the operating system.


5 Applications for SAN
  The new applications enabled by SAN technlogoy are actually new ways of
  organizing, accessing, and managing data. It is not that SAN technology
  introduces new accounting, transaction processing, Web server, electronic
  business or other techniques.


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    Application 1: Backup: Electronic business has essentially eliminated
     computer system idle time and sent developers on a search for less obtrusive
     solutions to the backup problem. With today’s technology, applications and
     database management systems must usually be made quiescent for an
     instant in order to get a backup started. This is an area for future
     development. Backups protect against hardware failures, software mal
     functions, and user errors. Volume managers and RAID subsystems are
     tending to assume more of a role in protecting against hardware failures. The
     role of backup in creating point in time images of enterprise data remains.
         o LAN free backup: Bulk data travels over a SAN. LAN free backup
             removes backup data transfers from the LAN, with the result that
             backup no longer affects the performance of un involved clients and
             servers. Use of SCSI.
         o Tape Drive Sharing: As you know that tape sharing is an expensive
             device. It is connected to directly to SAN where it can accessed by
             backup application to backup.
         o The Designated Backup Server: There is a designated server which
             will schedule the backup.
         o Server less backup: In this case, instead of the copying the data to
             server from the disk, server directly give the command to RAID asking
             this much of bulk data has to be copy, so it is directly handled.
         o Off – Host NAS Backup

    Application 2: Highly Available Data: Highly availability of data is a must for
     continuous computing. SAN Technology can be used to protect against a
     wider variety of threats to data integrity. RAID subsystem based protection
     against hardware failure can be augmented by server based volume
     management to create snapshots of operational data for mining and impact
     free backup purposes.
         o Mirroring 101: Technique of mirroring the data when one server writes
            data on to one disk will be automatically replicated to other.

    Application 3: Disaster Recoverability: The data is stored in two different
     physical locations where data distribution will be started.

    Application 4: Clusters – Continuous Computing: Cluster technology
     organizes the resources required to run an application and manages failover
     from one server to another. Failover may be automatic, as when a server fails
     and its applications are restarted on an alternate server, or manual, in which


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      an administrator forces an application to migrate from one server to another
      for maintenance purpose.
     Application 5: Data Replication: Data replication technology can be used to
      enable recovery from site disasters, for publication or consolidation of data in
      a distributed enterprise, or for moving data from one server to another.
      Variations of replication technology are used to replicate volumes, files and
      directory and databases.

          Replication technology differs from mirroring in that it is designed to work
      with unreliable connections between primary and secondary sites and
      designed for situations in which the time required to propagate updates to
      secondary sites cannot be part of applications response time.


6 Storage Network Architecture
  The Volume: Disks are often logically combined by software that uses mirroring,
  RAID, and striping techniques to improve their net storage capacity, reliability, or
  I/O performance characteristics. Software that combines disks in this way
  presents disk-like storage entities to its clients. These disk-like entities are
  commonly known as volumes, logical units (abbreviated LUNs, for the numbers
  by which logical units are identified in popular I/O protocols), or virtual disks.

  BASIC SAN MODEL

  The figure illustrates the basic SAN data access model for a simple system with
  a SAN In this system, the file system runs in the application server. Volume
  functionality would typically be provided by external RAID controllers attached to
  the SAN, possibly augmented by a server-based volume manager.




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7 Storage System
  In order to understand the storage systems, it is important to understand the disk
  drives, the most common building block of system systems, and the disk drive
  interface technologies used.

  The storage devices include RAID disk arrays, Just a Bunch Of Disks (JBODs),
  tape systems, Network Attached Storage Systems, optical storage systems etc.
  The type of interfaces provided on these devices includes SCSI, Fibre Channel,
  and Ethernet.


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    Disk Drive Interfaces
        o ATA
        o SATA
        o SCSI
        o SAS
        o Fibre Channel
        o JBOD
        o RAID

 ATA: ATA is the primary internal storage interface for the PC, connecting the
 host system to peripherals such as hard drives, optical drives, CD-ROMs
 SATA: Serial ATA is the next generation internal storage inter connect designed
 to replace Ultra ATA. The SATA interface is an evolution of the ATA interface
 from parallel bus to serial bus architecture. The serial bus architecture
 overcomes the difficult electrical constraints hindering continued speed
 enhancement of the parallel ATA bus.
 SCSI: Small Computer System Interface (SCSI) defines a universal, parallel
 system interface, called the SCSI bus, for connecting up to eight devices along a
 single cable. SCSI is an independent and intelligent local I/O bus through which a
 variety of different devices and one or more controllers can communicate and
 exchange information independent of the rest of the system.
 SAS: To overcome the bandwidth barrier of parallel bus cabling, the Serial
 Attached SCSI (SAS) is being defined to replace the physical layer of SCSI with
 serial bus technology. SAS is a new near-cabinet and disk interface technology
 that leverages the best of the SCSI and serial ATA interfaces to bring new
 capabilities, higher levels of availability, and more scalable performance to future
 generations of servers and storage systems. SAS uses a serial, point-to-point
 topology to overcome the performance barriers associated with storage systems
 based on parallel bus or arbitrated loop architectures
 Fibre Channel: Fibre Channel Disk Drives typically come with single or dual
 Fibre Channel Arbitrated Loop (FC-AL) interfaces. The dual FC-AL interface is
 useful in storage systems for providing redundant cabling. Some drives even
 allow concurrent access from the two interfaces to increase the bandwidth to the
 drive. fabric. Using the FC-AL protocol, a large number of disk drives can be
 connected together for large capacity storage systems. All the devices on the
 loop share the bandwidth of the loop. To prevent a single point of failure in the
 physical loop topology, the disk drives in a storage system are typically
 connected to a central Port Bypass Controller (PBC) in a star topology.
 RAID: RAID (Redundant Array of Independent Disks) is a technology to combine
 multiple small, independent disk drivers into an array that looks like a single, big
 disk drive to the system. Simply putting n disk drives together (as in JBOD)
 results in a system with a failure rate that is n times the failure rate of a single
 disk. The high failure rate makes the disk array concept impractical for
 addressing the high reliability and large capacity needs of enterprise storage.



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