Storage Area Networking SAN NAS Fibre Channel iSCSI

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Saturday, December 16, 2006

Storage Area Networking Jobs Interview Questions

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Fibre Channel Network Adapter Card
(Host Bus Adapter- HBA)

Fibre Channel Cable

FC Cable in comparison with a Serial DB9 Cable

After listing more than 60 interview questions in the previous posts find below some listing of only questions from storage interviews. Answers for the same will be sent only through email if you contribute for this blog. Below questions are contributed by Jai one of the professional working in Real Storage Job who contributed this posting.

1)What is the most critical component in SAN?
2)What is the default id for SCSI HBA?
3)What is parallelism?
4)What do you know about SAN testing?
5)Explain a typical SAN landscape?
6)What is fan-in and fan-out in SAN Virtualization system?
7)How is the interoperability between the server and the storage is achieved?
8)What are the performance metrics of SAN?
9)What do you know about I/O meters , their types and how are the used?
10)What is the equivalent of Address resolution protocol in storage?
11)What is meant by availability & reliability in Storage ?
12)What is Disaster Recovery & how it is implemented in a Storage environment?
13)Example for failover cluster configurations ?
14)What are the needs/advantages of Storage consolidation ?


Storage area networking Interview Questions

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Some more interview questions contributed by Jai
51) What is one of the constrains of using storage switch?

52) What is the difference between NAS and SAN?

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

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

53) 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

54) 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.

55) 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.

56) 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 the additional overhead of monitoring multiple connections and to see whether a particular request is completed.

57) 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.

58) Explain different types of RAID?
RAID 0: data striping blocks are written sequentially, no redundancy, high performance than single disk access.

RAID 1: Mirroring, data blocks written to both disk at once, 100% redundancy, 100% additional capacity required. Read can be distributed across both the disks to increase performance.

RAID 3: Striping with byte parity, adds parity information to rebuild data in the event of disk failure, high transfer rate and availability with lower capacity required than RAID 1. Transactions performance low because all disks operate in lock step.

RAID 4: striping with block parity, independently accessible disks, data blocks written sequentially to each disk failure. Dedicated parity disk is write bottleneck and leads to poor performance.

RAID 5: Striping with rotational parity, parity blocks written per row and distributed across all disks, parity distribution eliminates single write bottleneck overhead for parity calculation on write supplemented with parallel microprocessors or caching.

59) 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. Abbreviated NAS. 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.

60)Briefly list the advantages of SAN ?
SANs fully exploit high-performance, highconnectivity 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)


Storage jobs interview questions from real interview experiences

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Simple interview questions with very simple answers from Real Storage Job interviews : Contributed by Jai

I would request you all to contribute any text,post,article for this blog & help the people struggling for a Job in Networking,Storage,System administration - You will get more than 200 interview questions inreturn for your contribution.

Some more interview questions are listed below
40) What is Exchange in FC(Fibre Channel)?
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

41) 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

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

43) What are three levels of management in storage?
a) Storage Level Management
b) Network Level Management
c) Enterprise Level Management.

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

45) 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.

46) What is the measuring unit of data activity?
Gigabits per hour

47) What are the basic storage policies?
a) Security and authentication
b) Capacity, Content and quota management
c) Quality of Service

48) 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).

49) Explain different classes of service in FC?
Class 1: dedicated connection between two communicators with acknowledgement of frame delivery.
Class 2: is connection less but provides acknowledgement
Class 3: is connection less and provides no notification of delivery
Class 4: allows fractional bandwidth for virtual circuits
Class 5: Provides multicast with acknowledgment
Class F: Is used for switch to switch communication in the fabric.

50) 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.

More than 40 interview questions on storage,san,nas,FC:Thanks Jai for this contribution

I want to thank Jai one of our blog reader who has contributed more than 58 interview questions from his experience of attending real storage interviews.

In the last 2 posts we had more than 30 interview questions posted which can be accessed through the below links
interview questions Series 1
interview questions Series 2

Here you get 10 more interview questions for storage area networking
31) What are tow types of recording techniques on the tapes?
a) Linear Recording
b) Helical Scan Recording.

32) What is snap shot?
A snapshot of data object contains an image of data at a particular point of time.

33) What is HSM?
Hierarchical storage management, an application that attempts to match the priority of data with the cost of storage.

34) What is hot-swapping?
Devices are allowed to be removed and inserted into a system without turning off the system.

35) What is Hot-Sparing?
A spare device is available to be inserted into the subsystem operation without having to remove and replace a device.

36) What are different types of backup system?
a) Offline
b) Online
c) Near Line

37) What is the different between mirroring, Routing and multipathing?

Redundancy Functions Relationships Role
Mirroring Generates 2 i/os 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

38) Name few types of Tape storage?
a) Digital Linear Tape
b) Advanced Intelligent Tape
c) Linear Tape Open

39) What is a sequence in FC?
Group of one or more frames that encompasses one or more “information units” of a upper layer protocol.

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.

40) 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

Networking (Storage) interview questions contributed by Jai(series 2)

Continuing the previous posting here some more interview questions contributed by our blog reader Jai.
More than 20 real storage job interview questions were posted in the previous post.

21) 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.

22) 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.

23) 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.

24) What is Multipath I/O?
Fault tolerant technique where by 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.

25) 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.

26) 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.

27) What is LUN Masking?
A method used to create an exclusive storage area and access control. And this can be achieved bye storage device control program.

28) What is the smallest unit of information transfer in FC?

29) How is the capacity of the HDD calculated?
Number of Heads X Number of Cylinders X Sectors per track X Sector Size

30) 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).

Real Interview Questions contributed by blog reader Jai

Hearty thanks to this blog's reader Jai who has contributed more than 58 interview questions from his experience of attending interviews for real company jobs.

I will be posting these questions in the subsequent blog postings - I rally appreciate his initiative and would request all other professionals or whoever - who have the knowledge to share it with the community and help the jobseekers.

1) What is the difference between RAID 0, RAID 1 and RAID 5?

RAID 0 => Plain striping typically with 24kb, 54kb or 128kb stripe size
RAID 1 => Mirroring
RAID 5 => Stripping with parity

2) Describe in brief the composition of FC Frame?
Start of the Frame locator
Frame header (includes destination id and source id, 24 bytes/6 words)
Data Payload (encapsulate SCSI instruction can be 0-2112 bytes in length)
CRC (error checking, 4 bytes)
End of Frame (1 byte)

3) What is storage virtualization?
Storage virtualization is amalgamation of multiple n/w storage devices into single storage unit.

4) What are the protocols used in physical/datalink and network layer of SAN?
a) Ethernet
c) Fibre Channel

5) What are the types of disk array used in SAN?

6) What are different types of protocols used in transportation and session layers of SAN?
a) Fibre Channel Protocol (FCP)
b) Internet SCSI (iSCSI)
c) Fibre Channel IP (FCIP)

7) What is the type of Encoding used in Fibre Channel?
8b/10b, as the encoding technique is able to detect all most all the bit errors

8) How many classes of service are available in Fibre Channel?
7 Classes of service

9) What are the main constrains of SCSI in storage networking?
a) Deployment distance (max. of 25 mts)
b) Number of devices that can be interconnected (16)

10) What is a Fabric?
Interconnection of Fibre Channel Switches

11) 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

12) 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.

13) What are the different topologies in Fibre Channel?
a) Point-to-Point
b) Arbitrary Loop
c) Switched Fabric Loop

14) 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

15) 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.

16) What are the two major classification of zoning?
Two types of zoning are
a) Software Zoning
b) Hardware Zoning

17) 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

18) What are the 3 prominent characteristics of SAS Protocol?
a) Native Command Queuing (NCQ)
b) Port Multiplier
c) Port Selector

19) 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

20) How does FC Switch maintain the addresses?
FC Switch uses simple name server to maintain the mapping table

Storage Area Network and Network Attached Storage

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