SAN INTERVIEW QUESTIONS-->2

SAN Interview Questions and Answers

21. FC Controllers: These are Data transfer media they will sit on PCI slots of Server; you can configure Arrays and volumes on it?

JBOD: Just Bunch of Disks is Storage Box, it consists of Enclosure where set of hard-drives are hosted in many combinations such SCSI drives, SAS, FC, SATA.

22. What is the most critical component in SAN?

Each component has its own criticality with respect to business needs of a company.

23. How is a SAN managed?

There are many management software’s used for managing SAN's to name a few
- Santricity
- IBM Tivoli Storage Manager.
- CA Unicenter.
- Veritas Volumemanger.

24. Which one is the Default ID for SCSI HBA?

Generally the default ID for SCSI HBA is 7.
SCSI- Small Computer System Interface
HBA - Host Bus Adaptor


25. What is the highest and lowest priority of SCSI?

There are 16 different ID’s which can be assigned to SCSI device 7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, 8.

Highest priority of SCSI is ID 7 and lowest ID is 8.

26. How do you install device drivers for the HBA first time during OS installation?

In some scenarios you are supposed to install Operating System on the drives connected thru SCSI HBA or SCSI RAID Controllers, but most of the OS will not be updated with drivers for those controllers, that time you need to supply drivers externally, if you are installing windows, you need to press F6 during the installation of OS and provide the driver disk or CD which came along with HBA.
If you are installing Linux you need to type "linux dd" for installing any driver.


27. What is Array?

Array is a group of Independent physical disks to configure any Volumes or RAID volumes.

28. Can u describe at-least 3 troubleshooting scenarios which you have come across in detail ?

SCENARIO 1: How do you find/debug when there is error while working SCSI devices?

In our daily SAN troubleshooting there are many management and configuration tools we use them to see when there is a failure with target device or initiator device.
Some time it is even hard to troubleshoot some of the things such as media errors in the drives, or some of the drives taking long time to spin-up. In such cases these utilities will not come to help. To debug this kind of information most of the controller will be implemented with 3-pin serial debug port. With serial port debug connector cable you can collect the debug information with hyper terminal software.

SCENARIO 2: I am having an issue with a controller its taking lot of time to boot and detect all the drives connected how can I solve this.?

There are many possibilities that might cause this problem. One of the reason might be you are using bad drives that cannot be repaired. In those cases you replace the disks with working ones.

Another reason might be slots you connected your controller to a slot which might not be supported.
Try to connect with other types of slots.

One more probable reason is if you have flashed the firmware for different OEM’s on the same hardware.
To get rid of this the flash utilities will be having option to erase all the previous and EEPROM and boot block entry option. Use that option to rectify the problem.

SCENARIO 3: I am using tape drive series 700X, even the vendor information on the Tape drive says 700X, but the POST information while booting the server is showing as 500X what could be the problem?

First you should make sure your hardware is of which series, you can find out this in the product website.
Generally you can see this because in most of the testing companies they use same hardware to test different series of same hardware type. What they do is they flash the different series firmware. You can always flash back to exact hardware type.

29. Which are the SAN topologies?

SAN can be connected in 3 types which are mentioned below:
Point to Point topology
FC Arbitrated Loop ( FC :Fibre Channel )
Switched Fabric
30. Which are the 4 types of SAN architecture types?

 a. Core-edge b. Full-Mesh

 c. Partial-Mesh

 d. Cascade

31. Which command is used in linux to know the driver version of any hardware device?

dmesg

32. How many minimum drives are required to create R5 (RAID 5) ?


You need to have at least 3 disk drives to create R5.

33. Can you name some of the states of RAID array?

There are states of RAID arrays that represent the status of the RAID arrays which are given below
a. Online
b. Degraded
c. Rebuilding
d. Failed

34. Name the features of SCSI-3 standard?


QAS: Quick arbitration and selection

Domain Validation
CRC: Cyclic redundancy check

35. Can we assign a hot spare to R0 (RAID 0) array?

No, since R0 is not redundant array, failure of any disks results in failure of the entire array so we cannot rebuild the hot spare for the R0 array.

36. Can you name some of the available tape media types?

There are many types of tape media available to back up the data some of them are
DLT: digital linear tape - technology for tape backup/archive of networks and servers; DLT technology addresses midrange to high-end tape backup requirements.
LTO: linear tape open; a new standard tape format developed by HP, IBM, and Seagate.
AIT: advanced intelligent tape; a helical scan technology developed by Sony for tape backup/archive of networks and servers, specifically addressing midrange to high-end backup requirements.

37. What is HA?

HA High Availability is a technology to achieve failover with very less latency. Its a practical requirement of data centers these days when customers expect the servers to be running 24 hours on all 7 days around the whole 365 days a year - usually referred as 24x7x365. So to achieve this, a redundant infrastructure is created to make sure if one database server or if one app server fails there is a replica Database or Appserver ready to take-over the operations. End customer never experiences any outage when there is a HA network infrastructure.

38. What is virtualization?

Virtualization is logical representation of physical devices. It is the technique of managing and presenting storage devices and resources functionally, regardless of their physical layout or location. Virtualization is the pooling of physical storage from multiple network storage devices into what appears to be a single storage device that is managed from a central console. Storage virtualization is commonly used in a storage area network (SAN). The management of storage devices can be tedious and time-consuming. Storage virtualization helps the storage administrator perform the tasks of backup, archiving, and recovery more easily, and in less time, by disguising the actual complexity of the SAN.

39. 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)


40. What is storage virtualization?

Storage virtualization is amalgamation of multiple n/w storage devices into single storage unit.

41. What are the protocols used in physical/datalink and network layer of SAN?

 a) Ethernet
 b) SCSI
 c) Fibre Channel

42. What are the types of disk array used in SAN?

a) JBOD
b) RAID

43. 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)

44. 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

45. How many classes of service are available in Fibre Channel?

 7 Classes of service are available in Fibre Channel

Class-1: Dedicated connection between two communicators with acknowledgement of frame delivery.
In class 1 service, a dedicated connection source and destination is established through the fabric for the duration of the transmission. It provides acknowledged service. This class of service ensures that the frames are received by the destination device in the same order in which they are sent, and reserves full bandwidth for the connection between the two devices. It does not provide for a good utilization of the available bandwidth, since it is blocking another possible contender for the same device. Because of this blocking and necessary dedicated connection, class 1 is rarely used.

Class-2: connection less but provides acknowledgement
Class 2 is a connectionless, acknowledged service. Class 2 makes better use of available bandwidth since it allows the fabric to multiplex several messages on a frame-by-frame basis. As frames travel through the fabric they can take different routes, so class 2 service does not guarantee in-order delivery. Class 2 relies on upper layer protocols to take care of frame sequence. The use of acknowledgments reduces available bandwidth, which needs to be considered in large-scale busy networks.

Class-3: connection less and provides no notification of delivery
There is no dedicated connection in class 3 and the received frames are not acknowledged. Class 3 is also called datagram connectionless service. It optimizes the use of fabric resources, but it is now upper layer protocol to ensure that all frames are received in the proper order, and to request to the source device the retransmission of missing frames. Class 3 is a commonly used class of service in Fibre Channel networks.

Class-4: allows fractional bandwidth for virtual circuits
Class 4 is a connection-oriented service like class 1, but the main difference is that it allocates only a fraction of available bandwidth of path through the fabric that connects two N_Ports. Virtual Circuits (VCs) are established between two N_Ports with guaranteed Quality of Service (QoS), including bandwidth and latency. Like class 1, class 4 guarantees in-order delivery frame delivery and provides acknowledgment of delivered frames, but now the fabric is responsible for multiplexing frames of different VCs. Class 4 service is mainly intended for multimedia applications such as video and for applications that allocate an established bandwidth by department within the enterprise. Class 4 was added in the FC-PH-2 standard.

Class -5: Class 5 is called isochronous service, and it is intended for applications that require immediate delivery of the data as it arrives, with no buffering. It is not clearly defined yet. It is not included in the FC-PH documents.

Class-6: Provides multicast, dedicated connection with acknowledgment
Class 6 is a variant of class 1, known as multicast class of service. It provides dedicated connections for a reliable multicast. An N_Port may request a class 6 connection for one or more destinations. A multicast server in the fabric will establish the connections and get acknowledgment from the destination ports, and send it back to the originator. Once a connection is established, it should be retained and guaranteed by the fabric until the initiator ends the connection. Class 6 was designed for applications like audio and video requiring multicast functionality. It appears in the FC-PH-3 standard.

Class-F: used for switch to switch communication in the fabric.
Class F service is defined in the FC-SW and FC-SW-2 standard for use by switches communicating through ISLs. It is a connectionless service with notification of non-delivery between E_Ports used for control, coordination, and configuration of the fabric. Class F is similar to class 2; the main difference is that Class 2 deals with N_Ports sending data frames, while Class F is used by E_ports for control and management of the fabric.