SAN Fundamentals - 2

FAQS

64. What are the services provided by Fabric to all the nodes?

a) Fabric Login b) SNS c) Fabric Address Notification d) Registered state change notification e) Broadcast Servers

65. What is the difference between LUN and WWN?

LUN: unique number that is assigned to each storage device or partition of the storage that the storage can support.
WWN: 64bit address that is hard coded into a fibre channel HBA and this is used to identify individual port (N_Port or F_Port) in the fabric.

66. What are the different topologies in Fibre Channel?

 a) Point-to-Point
b) Arbitrary Loop
c) Switched Fabric Loop

67. What are the layers of Fibre Channel Protocol?

 a) FC Physical Media
b) FC Encoder and Decoder
c) FC Framing and Flow control
d) FC Common Services
e) FC Upper Level Protocol Mapping

68. What is zoning?

Fabric management service that can be used to create logical subsets of devices within a SAN. This enables portioning of resources for management and access control purpose.

69. What are the two major classification of zoning?

Two types of zoning are
a) Software Zoning
b) Hardware Zoning

70. What are different levels of zoning?

 a) Port Level zoning
b) WWN Level zoning
c) Device Level zoning
d) Protocol Level zoning
e) LUN Level zoning

71. What are the 3 prominent characteristics of SAS Protocol?

 a) Native Command Queuing (NCQ)
b) Port Multiplier
c) Port Selector

72. What are the 5 states of Arbitrary Loop in FC?

 a) Loop Initialization
b) Loop Monitoring
c) Loop arbitration
d) Open Loop
e) Close Loop

73. How does FC Switch maintain the addresses?

FC Switch uses simple name server (SNS) to maintain the mapping table

74. What is the purpose of disk array?

Probability of unavailability of data stored on the disk array due to single point failure is totally eliminated.

75. What is disk array?

Set of high performance storage disks that can store several terabytes of data. Single disk array can support multiple points of connection to the network.

76. What is virtualization?

A technique of hiding the physical characteristics of computer resources from the way in which other system application or end user interact with those resources. Aggregation, spanning or concatenation of the combined multiple resources into larger resource pools.

77. What is Multipath I/O?

Fault tolerant technique where, there is more than one physical path between the CPU in the computer systems and its main storage devices through the buses, controllers, switches and other bridge devices connecting them.

78. What is RAID?

Technology that groups several physical drives in a computer into an array that you can define as one or more logical drive. Each logical drive appears to the operating system as single drive. This grouping enhances the performance of the logical drive beyond the physical capability of the drives.

79. What is stripe-unit-size?

It is data distribution scheme that complement s the way operating system request data. Granularity at which data is stored on one drive of the array before subsequent data is stored on the next drive of the array. Stripe unit size should be close to the size of the system I/O request.

80. What is LUN Masking?

A method used to create an exclusive storage area and access control. And this can be achieved by storage device control program.

81. What is the smallest unit of information transfer in FC?

Frame

82. How is the capacity of the HDD calculated?

Number of Heads X Number of Cylinders X Sectors per track X Sector Size

83. What is bad block reallocation?

A bad sector is remapped or reallocated to good spare block and this information is stored in the internal table on the hard disk drive. The bad blocks are identified during the media test of the HDD as well as during various types of read write operations performed during the I/O tests. Apart from the new generation of HDD comes with a technology called BGMS (background media scan) which continuously scans the HDD media for defects and maps them when the drive is idle (this is performed after the HDD is attached to the system).

84. What are two types of recording techniques on the tapes?

a) Linear Recording
b) Helical Scan Recording.

85. What is snapshot?

A snapshot of data object contains an image of data at a particular point of time.

86. What is HSM?

Hierarchical storage management - An application that attempts to match the priority of data with the cost of storage.

87. What is hot-swapping?

Devices are allowed to be removed and inserted into a system without turning off the system.

88. What is Hot-Sparing?

A spare device is available to be inserted into the subsystem operation without having to remove and replace a device.

89. What are different types of backup system?

a) Offline
b) Online
c) Near Line

90. What is the different between mirroring, Routing and multipathing?

Redundancy Functions Relationships Role
Mirroring Generates 2 ios to 2 storage targets Creates 2 copies of data
Routing Determined by switches independent of SCSI Recreates n/w route after a failure
Multipathing Two initiator to one target Selects the LUN initiator pair to use.

91. Name few types of Tape storage?

 a) Digital Linear Tape
b) Advanced Intelligent Tape
c) Linear Tape Open

92. What is a sequence in FC?

Group of one or more frames that encompasses one or more “information units” of a upper layer protocol.
Example:
It requires
i) One sequence to transfer the command
ii) One or more sequence to transfer the data
iii) Once sequence to transfer the status.

93. What is Exchange in FC?

Exchange is to establish a relationship between 2 N_PORTs and then these two ports transfer data via one or more sequence within this relationship.
Example: Exchange exist to transfer the command, data and the status of one SCSI task

94. Why do we need Login in FC?

Port Login: To exchange service parameters between N_Ports and N_Ports
Process Login: To establish the SCSI operating environment between two N_PORTS
Fabric Login: Similar to port login, FLOGI is an extended link service command that sets up a session between two participants. With FLOGU a session is created between an N_Port or NL_Port and the switch.

95. What are the different types of clusters?

 a) High availability clusters
b) High Performance Clusters
c) Load Balancing Clusters.

96. What are three levels of management in storage?

 a) Storage Level Management
b) Network Level Management
c) Enterprise Level Management

97. What are the key activities in SAN management?

 a) Monitoring
b) Configuring
c) Controlling
d) Troubleshooting
e) Diagnosing

98. What is the difference between HBA and NIC?

HBA => Host bus adapters are used in storage based traffic while NIC (Network Interface Cards are used in IP based LAN traffic.

99. What is the measuring unit of data activity?

Gigabits per second (Gb/ps)

100. What are the basic storage policies?

 a) Security and authentication
b) Capacity, Content and quota management
c) Quality of Service

101. What is bypass circuitry?

A circuit that automatically removes the storage device from the data path (FC device out of FC AL loop) when signaling is lost (this signal is called port by-pass signal).

102. How many connections are possible in Fabric topology?

2^24 (24 bit address to the port), and the largest possible fabric will have 239 interconnected switches.

103. What is one of the constrain of using storage switch?

Latency

104. What is the difference between NAS and SAN?

NAS
Cables used in the n/w
n/w protocols (TCP/IP, IPx) and file sharing protocols (CIFS & NFS)
Lower TCO
Support heterogeneous clients
Slow

SAN
High-speed connectivity such as FC
Do not use n/w protocols because data request are not made over LAN
Higher TCO
Requires special s/w to provide access to heterogeneous clients
Fast

105. What is Jitter?

Jitter refers to any deviation in timing that a bit stream suffers as it traverses the physical medium and the circuitry on-board the end devices. A certain amount of deviation from the original signaling will occur naturally as serial bit stream propagates over fibre-optic or copper cabling. Mainly caused by electro-magnetic interference

106. What is BER/Bit error rate?

Probability that a transmitted bit will be erroneously received is the measure of number of bits (erroneous) at the output of the receiver and dividing by the total number of bits in transmission.

107. What is WWPN?

WWPN is the 16bit character that is assigned to the port, SAN volume controller uses it to uniquely identify the fibre channel HBA that is installed in the host system.

108. What is burst Length?

The burst length is the number of bytes that the SCSI initiator sends to the SCSI target in the FCP_DATA sequence.

109. What is NAS in detail?

NAS or Network Attached Storage

“NAS is used to refer to storage elements that connect to a network and provide file
access services to computer systems. A NAS Storage Element consists of an interface or engine, which implements the file services, and one or more devices, on which data is stored. NAS elements may be attached to any type of network. When attached to SANs, NAS elements may be considered to be members of the SAS (SAN Attached Storage) class of storage elements.
A class of systems that provide file services to host computers. A host system that uses network attached storage uses a file system device driver to access data using file access protocols such as NFS or CIFS. NAS systems interpret these commands and perform the internal file and device I/O operations necessary to execute them.
Though the NAS does speed up bulk transfers, it does not offload the LAN like a SAN does. Most storage devices cannot just plug into gigabit Ethernet and be shared - this requires a specialized file server the variety of supported devices is more limited.NAS has various protocols established for such needed features as discovery, access control, and name services.

110. Briefly list the advantages of SAN?

SANs fully exploit high-performance, high connectivity network technologies
SANs expand easily to keep pace with fast growing storage needs
SANs allow any server to access any data
SANs help centralize management of storage resources
SANs reduce total cost of ownership (TCO).
iSCSI fundamentals
iSCSI is a protocol defined by the Internet Engineering Task Force (IETF) which enables SCSI commands to be encapsulated in TCP/IP traffic, thus allowing access to remote storage over low cost IP networks.

111. What advantages would using an iSCSI Storage Area Network (SAN) give to your organization over using Direct Attached Storage (DAS) or a Fibre Channel SAN?

 · iSCSI is cost effective, allowing use of low cost Ethernet rather than expensive Fibre architecture.
· Traditionally expensive SCSI controllers and SCSI disks no longer need to be used in each server, reducing overall cost.
· Many iSCSI arrays enable the use of cheaper SATA disks without losing hardware RAID functionality.
· The iSCSI
· The iSCSI storage protocol is endorsed by Microsoft, IBM and Cisco, therefore it is an industry standard.
· Administrative/Maintenance costs are reduced.
· Increased utilisation of storage resources.
· Expansion of storage space without downtime.
· Easy server upgrades without the need for data migration.
· Improved data backup/redundancy.



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