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Block Level Transfer:

Presentation of storage can be formatted and managed as local drive.

Ex: A windows host that has been given a storage from SAN identifies the storage as a local disk and host is allowed to format the disk.

In this block level storage, raw volumes of storage are created and each block can be controlled as an individual hard drive. These Blocks are controlled by server based operating systems and each block can be individually formatted with the required file system.

SAN needs to be connected to an OS and then shared to users.

  • Block level storage is usually deployed in SAN or storage area network environment.
  • This level of storage offers boot-up of systems which are connected to them.
  • Block level storage can be used to store files and can work as storage for special applications like databases, Virtual machine file systems and so on.
  • Block level storage data transportation is much efficient and reliable.
  • Block level storage supports individual formatting of file systems like NFS, NTFS or SMB (Windows) or VMFS (VMware) which are required by the applications.
  • Each storage volume can be treated as an independent disk drive and it can be controlled by external server operating system.
  • Block level storage uses iSCSI and FCoE protocols for data transfer as SCSI commands act as communication interface in between the initiator and the target.

File level transfter:

Presentation of storage that is formatted and is managed from the host presenting the storage.

Ex: windows host mapped to shared directory doesnt have ability to format it.

This storage technology is common to storage system, which is found in hard drives, NAS systems and so on. In this File Level storage, the storage disk is configured with a protocol say NFS or SMB/CIFS and the files are stored and accessed from it in bulk.

  • The File level storage is simple to use and implement.
  • It stores files and folders and the visibility is the same to the clients accessing and to the system which stores it.
  • This level storage is inexpensive to be maintained, when it is compared to its counterpart i.e. block level storage.
  • Network attached storage systems usually depend on this file level storage.
  • File level storage can handle access control, integrate integration with corporate directories; and so on.

LUN: A LUN is a Logical Unit Number. It can be used to refer to an entire physical disk, or a subset of a larger physical disk or disk volume. The physical disk or disk volume could be an entire single disk drive, a partition (subset) of a single disk drive, or disk volume from a RAID controller comprising multiple disk drives aggregated together for larger capacity and redundancy. LUNs represent a logical abstraction or, if you prefer, virtualization layer between the physical disk device/volume and the applications.

Storage Area Network:

A storage area network (SAN) is a high-speed special-purpose network (or subnetwork) that interconnects different kinds of data storage devices with associated data servers on behalf of a larger network of users.

storage area network (SAN) is a dedicated network that provides access to consolidated, block level data storage. SANs are primarily used to make storage devices, such as disk arraystape libraries, and optical jukeboxes, accessible to servers so that the devices appear like locally attached devices to the operating system. A SAN typically has its own network of storage devices that are generally not accessible through the local area network by other devices.

SAN has dedicated connection to the machine using it. No file system. Just block of data. So there is a flexibility, you connect to windows machine, it uses NTFS. If you connect it to Unix/Linux, it uses ext3. So there is no file system dependency. In SAN env, we use Fibre channel and a dedicated line is laid from the storage box to the FC switch and from switch to the system(or server) that the Storage is connected. From that server, it storage is distributed to the users.

Typically, a storage area network is part of the overall network of computing resources for an enterprise. A storage area network is usually clustered in close proximity to other computing resources such as IBM z990 mainframes but may also extend to remote locations for backup and archival storage, using wide area network carrier technologies such as ATMor SONET.

A storage area network can use existing communication technology such as IBM’s optical fiber ESCON or use Fibre Channel technology. Some SAN system integrators liken it to the common storage bus (flow of data) in a personal computer that is shared by different kinds of storage devices such as a hard disk or a CD-ROM player.

SANs support disk mirroring, backup and restore, archival and retrieval of archived data, data migration from one storage device to another and the sharing of data among different servers in a network. SANs can incorporate subnetworks with network-attached storage (NAS) systems.

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  • Could be iSCSI or FC
  • FC san packages SCSI commands in to FC frames
  • servers connect to san using HBA
  • HBA connects to FC switch called Fabric
  • FC switch then connects to storage Processor (SP)
  • zones configured in FC switch define what HBA can connect to what SP and what LUN
  • Xenserver supports SAN Multipathing

We can set permissions at Fabric or at SP directing which xenserver can have access to which Fabric and to which LUNs.

Network Attached Storage:

Network-attached storage (NAS) is a dedicated hard disk storage device that is set up with its own network address and provides file-based data storage services to other devices on the network.

A network-attached storage device is attached to a local area network and assigned an IP address, allowing both application programming and files to be served faster because they are not competing for processor resources. NAS devices are usually configured with a web browser and do not have a keyboard or display. We have seen SAN is file system independent, in NAS we need to use CIFS or NFS only.

Network-attached storage consists of hard disk storage, including multi-disk RAID systems. NAS software can usually handle a number of network protocols, including Microsoft’sInternetwork Packet Exchange and NetBEUI, Novell’s Netware Internetwork Packet Exchange, and Sun Microsystems’ Network File System. Although some NAS boxes will run a standard operating system like Windows, many NAS devices run their own proprietary operating system. For example, the NAS platforms from NetApp use the company’s proprietary Data ONTAP operating system. Management utilities are able to manage heterogeneous multiple NAS boxes as more storage is added to the infrastructure, easing the management burden on storage administrators.

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Fiber Channel:

Fibre Channel is a technology for transmitting data between computer devices at data rates of up to 4 Gbps (and 10 Gbps in the near future). Fibre Channel is especially suited for connecting computer servers to shared storage devices and for interconnecting storage controllers and drives. Since Fibre Channel is three times as fast, it has begun to replace the Small Computer System Interface (SCSI) as the transmission interface between servers and clustered storage devices. Fibre channel is more flexible; devices can be as far as ten kilometers (about six miles) apart if optical fiber is used as the physical medium. Optical fiber is not required for shorter distances, however, because Fibre Channel also works usingcoaxial cable and ordinary telephone twisted pair.

Fibre Channel offers point-to-point, switched, and loop interfaces. It is designed to interoperate with SCSI, the Internet Protocol (IP) and other protocols, but has been criticized for its lack of compatibility – primarily because (like in the early days of SCSI technology) manufacturers sometimes interpret specifications differently and vary their implementations.

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iSCSI is Internet SCSI (Small Computer System Interface), an Internet Protocol (IP)-based storage networking standard for linking data storage facilities, developed by the Internet Engineering Task Force (IETF). By carrying SCSI commands over IP networks, iSCSI is used to facilitate data transfers over intranets and to manage storage over long distances. The iSCSIprotocol is among the key technologies expected to help bring about rapid development of the storage area network (SAN) market, by increasing the capabilities and performance of storage data transmission. Because of the ubiquity of IP networks, iSCSI can be used to transmit data over local area networks (LANs), wide area networks (WANs), or the Internet and can enable location-independent data storage and retrieval.


An initiator functions as an iSCSI client. An initiator typically serves the same purpose to a computer as a SCSI bus adapter would, except that, instead of physically cabling SCSI devices (like hard drives and tape changers), an iSCSI initiator sends SCSI commands over an IP network. An initiator falls into two broad types:

Software initiator

A software initiator uses code to implement iSCSI. Typically, this happens in a kernel-resident device driver that uses the existing network card (NIC) and network stack to emulate SCSI devices for a computer by speaking the iSCSI protocol. Software initiators are available for most popular operating systems and are the most common method of deploying iSCSI.

Hardware initiator

A hardware initiator uses dedicated hardware, typically in combination with software (firmware) running on that hardware, to implement iSCSI. A hardware initiator mitigates the overhead of iSCSI and TCP processing and Ethernet interrupts, and therefore may improve the performance of servers that use iSCSI.

Host bus adapter

An iSCSI host bus adapter (more commonly, HBA) implements a hardware initiator. A typical HBA is packaged as a combination of a Gigabit (or 10 Gigabit) Ethernet NIC, some kind of TCP/IP offload engine (TOE) technology and a SCSI bus adapter, which is how it appears to the operating system.

An iSCSI HBA can include PCI option ROM to allow booting from an iSCSI SAN.


The iSCSI specification refers to a storage resource located on an iSCSI server (more generally, one of potentially many instances of iSCSI storage nodes running on that server) as a target.

“iSCSI target” should not be confused with the term “iSCSI” as the latter is a protocol and not a storage server instance.

An iSCSI target is often a dedicated network-connected hard disk storage device, but may also be a general-purpose computer, since as with initiators, software to provide an iSCSI target is available for most mainstream operating systems.

How iSCSI works:

iSCSI uses iSCSI Qualified Name(IQN) t identify iSCSI targets and initiators.

When an end user or application sends a request, the operating system generates the appropriate SCSI commands and data request, which then go through encapsulation and, if necessary, encryption procedures. A packet header is added before the resulting IP packets are transmitted over an Ethernet connection. When a packet is received, it is decrypted (if it was encrypted before transmission), and disassembled, separating the SCSI commands and request. The SCSI commands are sent on to the SCSI controller, and from there to the SCSI storage device. Because iSCSI is bi-directional, the protocol can also be used to return data in response to the original request.

iSCSI is one of two main approaches to storage data transmission over IP networks; the other method, Fibre Channel over IP (FCIP), translates Fibre Channel control codes and data into IP packets for transmission between geographically distant Fibre Channel SANs. FCIP (also known as _Fibre Channel tunneling_or storage tunneling) can only be used in conjunction with Fibre Channel technology; in comparison, iSCSI can run over existing Ethernet networks. A number of vendors, including Cisco, IBM, and Nishan have introduced iSCSI-based products (such as switches and routers).

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Physical Block Device: An interface between physical host and an attached storage repository. Virtual Disk Image: The virtual storage that is presented to the virtual machine, where the OS is installed. Virtual Block Device: An object that maps virtual disk images to virtual machines.


  • iSCSI and Fiber Channel are protocols.
  • SAN and NAS are storages

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