The Storage Area Network (SAN)
It is the heart and soul of the storage industry which moves storage assets from a common network of users and restructures it into an independent, high-performance network. SANs are a committed high-speed subnetwork of shared storage devices providing access to integrated, block-level data storage. Their primary function is to further improve storage devices, such as disk arrays to access shared storage as if the devices appear directly attached to an operating system. Disk arrays in themselves can provide innovative data services such as multi-site replication and sub-LUN data tiered across contrasting physical disk types. Independent of how it is connected, whenever a host access a storage device on the SAN, it will send a block-based request for the storage device. This is especially true in enterprise environments where dozens if not hundreds of physical servers are connected to the same disk array.
Although, today’s most popular storage system interconnects are the Fibre Channel, iSCSI, and SAS, SAS is not usually considered a true SAN due primarily to distance and replication limitations across sites. Another option is the FCoE or Fibre Channel over Ethernet, but it is constrained only for converging IP (Internet Protocol) and SAN traffic in dense environments or conveying storage over extended links. However, any small quality business switches and NICs from NetGear, D-Link, Cisco / Linksys, etc. can be utilized to create a SAN.
This will leave native FC and iSCSI worthy of discussions for any storage needs needing replication or connectivity at distances of more than 30ft. and without question, a 1GB iSCSI is the least expensive SAN.
The Fibre Channel
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| 4.2 Fibre Channel (FC) SAN Components | Mycloudwiki |
Fibre Channel (FC) is a serial data transfer architecture for transmitting data between computer devices, oftentimes running at high-speed of 2, 4, 8, and 16 GB per second. Fibre Channel provides point-to-point, switched, and loop interfaces designed to interoperate with SCSI. It is suitable for linking computer servers to shared storage devices and for interconnecting storage controllers and drives. Since it is three times as fast, it has started to replace SCSI as the communication interface preferences between clustered storage devices. The most well-known Fibre Channel standard is Fibre Channel Arbitrated Loop (FC-AL) which was designed for new mass storage devices and other outlying devices that require extremely high bandwidth and can be as far as 10 kilometers apart if optical fiber is used as the physical medium. FCP or Fibre Channel Protocol is a transfer protocol, much like TCP used in IP networks that transfer SCSI commands over Fibre Channel networks.
In essence, Fibre Channel was used in supercomputers but has soon become a common connection fixture for storage area networks (SANs) storage. Despite its very suggestive name, signaling in Fibre channels can run on an electrical interface in addition to fiber-optic cables.
For all the myths clouding Fibre Channel, one is sure that it is not dead or even dying and it is here to stay even with the resurgence of iSCSI. One reason that Fibre Channel is alive, and kicking is notably the plan outlined by FCIA or Fibre Channel Industry Association for 32 GB specifications as a follow up to the 16 GB FC products entering the mainstream market in 2012.
Moreover, Fibre Channel traditionally has a built-in 3-generation backward compatibility, meaning an investment of 8Gb FC today will still be supported until a 128Gb FC is deployed, putting all anxieties in the dustbin whenever other extreme-FC devices develop all too quickly. The biggest threat to Fibre Channel is not iSCSI but Fibre Channel over Ethernet (FCoE), because FCoE architecture revolves around the fact that it is about getting “FC traffic to flow over the Ethernet wire and switches” resulting in a converged fabric. Cisco and Brocade switch already exist for linking FC HBAs and storage arrays to FCoE Converged Network Adapters.
One factor that may have contributed to the Fibre Channel’s mythical obsolescence might be the decisions of some storage vendors such as EMC and HP to change course away from utilizing Fibre Channel disk drives opting instead for SAS disk drives. It should be noted that in the late 1990s, disk drives were shipped with dual-port SCA-40PIN fiber channel connectors, so it is natural to use drives with arrays utilizing FC backends but, since disk drives always communicate with controllers via the SCSI Protocol just like SAS disk did, there is no basis to linked drives via Fibre Channel. Another compelling reason is to drive costs down, thus making disk drives manufacturers such as Hitachi and Seagate work with EMC and HP with the sole purpose of qualifying SAS drives for use in storage enclosures and JBODs but not in a RAID configuration. SAS drives can be used in workstations, servers, and desktops in contrast to FC drives which were usually reserved for storage arrays only.
The iSCSI
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| What is iSCSI? | How does it work? (Architecture, Components & Benefits) | Photo Source: educba.com |
iSCSI, short for Internet Small Computer System Interface, is an Internet Protocol-based (IP) storage linking standard for data storage systems over a network and facilitating data transfers by conveying SCSI commands over IP networks. iSCSI is a network protocol built on top of the TCP/IP networking protocol. iSCSI assists in transmitting data in a Gigabit Ethernet (GbE) interface at the physical layer, allowing systems bearing iSCSI to connect directly to IP routers and standard Gigabit Ethernet switches thereby allowing organizations or businesses to integrate storage devices into information center storage arrays. iSCSI can be operated over long distances by using existing system infrastructure and it runs over basically the same network devices that run the rest of the enterprise network.
When 10GbE was introduced to the market, comparing iSCSI to Fibre Channel was a no brainer, because comparing the cost of deploying a 1Gb iSCSI array like the VNXe3100 or VNXe300 disk expansion as opposed to 8 Gb HP P2000 G3 MSA Array Systems or EMC VNX5100 Entry-level SAN storage, the cost of Fibre Channel will surely soar since most businesses already have in their system 1Gb capable switches and NICs in place. The fairest approach to do a comparison is comparing a 10 GB iSCSI (10 GbE) with an 8 GB FC. The point here is that 8 GB FC is NOT more costly than a 10GbE, in fact in many instances it is cheaper. When 10GBaseT came into the market, it brings the value of 10 GB iSCSI downs, the 16 GB FC will have to cross the threshold of the mainstream market and will significantly offer faster speeds as a justification for the possibility of inflated cost due to small form-factor pluggable (SFPs) requirements. The 10GBaseT may be the game-changer here since SFPs won’t be necessary. The 10GBE will need CAT6 to reach 55 meters (180 ft.) and CAT6a is needed to reach the full distance of 100 meters (330 ft.) depending on the quality of installation.
A vital downside of FC SANs is the incapability to accommodate merged storage systems, except if that merged storage systems have had FC ports and Ethernet ports. The EMC VNXe3100 and EMC VNXe3300 Disk Expansion merged storage systems provide file storage (NFS and CIFS) besides adding to block-level storage iSCSI. In such cases, merged storage will give up the need to have a devoted file server on the network which in all possibilities may have been linked to the FC SAN.
Furthermore, EMC VNXe3100 and EMC VNXe3300 disk
expansion provide innovative file server features like compression right
within the storage file system to further boost performance.