Storage Concepts

Ø  Storage Tier

0 - Special Functionality

1 - Enterprise (15,000 rpm)

2 - Modular (10,000 rpm)

3 - General Purpose (7,200 rpm SATA)

Connectivity Tier :

A - Fibre Attached

B - iSCSI Attached (not yet available)

C - NAS (not yet available)

Ø  A SAN uses the SCSI(Small Computer Storage Interconnect) and FC (Fibre Channel) protocols to move data over a network and store it directly to disk drives in block format

Ø  Benefits of a SAN:

·         Removes the distance limits of SCSI-connected disks

·         Greater performance

·         Increased disk utilization

·         Higher availability to storage by use of multiple access paths

·         New disaster-recovery capabilities

·         Online recovery:

·         Reduction of servers

·         Increased input/output (I/O) performance and bulk data movement

·         Nondisruptive scalability

·         Storage on demand

What Makes a SAN ?

Ø  The parts: All the hardware you use to create a SAN; the switches, cables, disk arrays, and so forth

·         HBA , GBIC, Fiber-optic cables,

·         Hubs, Switches, Gateway, Router.

·         Storage arrays, Modular arrays, Monolithic arrays

Ø  The protocols: The languages that the parts use to talk to each other

·         Fibre Channel protocol, SCSI protocol

Ø  Modular arrays

·         Modular arrays come with shelves that hold the disk drives. Each shelf can hold between 10 to 16 drives Modular arrays usually fit into industry-standard 19" racks

·         Modular arrays almost always use two controllers with separate cache memory in each controller,and then mirror the cache between the controllers to prevent data loss. Mostmodern modular arrays have between 16 and 32GB of cache memory

Ø  Monolithic arrays

·         Monolithic arrays have many controllers, and those controllers can share direct access to a global memory cache (up to hundreds of gigabytes) of fast memory. This method of sharing access to a large global or monolithic cache is why these arrays are also called monolithic.

Ø  Gigabit Interface Converter (GBIC)

·         The GBIC is formally known as a transceiver;it can be a transmitter and a receiver.it has a laser inside that converts billions of digital bits into light pulses to be transmitted over optical fiber.In older HBAs, the transmission device was called a Gigabit Link Module (GLM) .two kinds of GBICs, defined by the wavelength of light that the laser inside generates: short-wave (500 m) and long-wave (10 km).

Ø  Cables

·         9μm, 50μm, and 62.5μm.

·         When 9μm cables are used to transmit data over long distances, they’re called dark fiber cables. That’s because you cannot see the laser light being transmitted with the naked eye, and if you ever did look into one of these cables, it would fry your eyeballs. Single-mode optical signals can travel much farther than multimode signals.

·         Cable connectors come in two different types. An SC connector (SC stands for Subscriber connector) is the standard optical connector for 1Gbit Fibre Channel. An LC connector (LC stands for Lucent connector) is standard for 2Gbit and 4Gbit Fibre Channel cable.

Ø  N_Ports (node ports), L_Ports (loop ports), G_Ports (global ports), F_Port (fabric port), FL_Port (fabric-to-loop port), E_Port (switch-to-switch expansion port) or a T_Port ( Trunk port), NL_port (node-to-loop port),

Ø  The disks inside a disk array are first arranged into RAID sets and then sliced up into partitions. The partitions are then assigned a LUN, and the LUN is assigned to a server in the SAN.

Ø  The WWN of the storage array is known as the World Wide Node Name or WWNN. The resulting WWN of the port on the storage array is known as the World Wide Port Name or WWPN.

Ø  no more than seven servers allocated per storage port (again, this is for each Gbps of bandwidth,but this is still a pretty good rule of thumb for even faster SAN components).Using this configuration allows those seven servers to share the connection and therefore the bandwidth of the storage port. This is commonly called the fan-in ratio of the storage port.

Ø  Having too many servers per port also means each port has only so many I/O operations it can support at one time (the maximum queue depth of the port). Most current storage arrays support at least 256 queues per port (some support 512). So if you want each server to be able to queue up 32 I/O operations at one time (which is a good best practice), limit the number of servers to eight per port (256/32 = 8). Most HBA vendors configure the default queue depth for their HBA drivers at 32 anyway, so this is a good default fan-in ratio for server-to-storage port.

Ø  An Infiniband adapter is called an HCA, or Host Channel Adapter; an iSCSI network card is called a TOE adapter, or TCP/IP Offload Engine adapter.

Ø  Multipathing Solutions:

·         Hewlett- Packard AutoPath, SecurePath

·         Microsoft MPIO

·         Hitachi Dynamic Link Manager

·         EMC PowerPath

·         IBM RDAC, MultiPath Driver

·         Sun MPXIO

·         VERITAS Dynamic Multipathing(DMP)

Ø  Zoning is also important because it can be used to keep storage of various servers separate from each other, keep SAN traffic localized within each zone, and separate different vendor storage arrays in the same fabric.zoning can be used as a method of making the SAN more secure.

✓ Soft zoning: Zones are identified by World Wide Name

✓ Hard zoning: Zones are identified by physical switch port