Sunday, 24 June 2012

SAN INTERVIEW QUESTIONS-->4

SAN Interview Questions and Answers


76. 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.

77. 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

78. 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.

79. What are the different types of clusters?
  
 a) High availability clusters
 b)
 High Performance Clusters
 c)
 Load Balancing Clusters.

80. What are three levels of management in storage?

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

81. What are the key activities in SAN management?
  
  a) Monitoring
  b)
 Configuring
  c)
 Controlling
  d)
 Troubleshooting
  e)
 Diagnosing

82. 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.
83. What is the measuring unit of data activity?

Gigabits per second (Gb/ps)

84. What are the basic storage policies?

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

85. 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).
86. 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.

87. What is one of the constrain of using storage switch?
Latency

88. 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
89. 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

90. 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.
91. 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.

92. What is connection allegiance?
Given multiple connections are established, individual command/response pair must flow over the same connection. This connection allegiance ensures that specific read or writes commands are fulfilled without any additional overhead of monitoring multiple connections and to see whether a particular request is completed.

93. 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.
94. 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.
95. 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).

96. 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 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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