SAN Interview Questions with Answers:-
1. Explain What is a SAN?
SAN is short for Storage Area Network. It is a high-speed network of storage elements, similar in form and function to a LAN that establishes direct and indirect connections between multiple servers and multiple storage elements. The SAN is an extension of the server’s storage bus
2. What does a SAN do?
SANs create connectivity. SANs offer a method of attaching storage that improves data reliability, availability, and performance
SAN overcomes traditional network bottlenecks by connecting in three ways:
- Server-to-storage (direct attached storage)
- Server-to-server (network attached storage)
- Storage-to-storage (SAN Attached Storage)
3. Name some of the SAN topologies and Explain each of them?
Point-to-point, arbitrated loop, and switched fabric topologies
a) Point-to-Point
A point-to-point connection is the simplest topology. It is used when there are
exactly two nodes and future expansion is not predicted. There is no sharing of the media, which allows the devices to use the total bandwidth of the link. A simple link initialization is needed before communications can begin.
b) Arbitrary Loop
Our second topology is Fiber Channel Arbitrated Loop (FC-AL). FC-AL is more
useful for storage applications. It is a loop of up to 126 nodes (NL_Ports) that is managed as a shared bus. Traffic flows in one direction, carrying data frames and primitives around the loop with a total bandwidth of 400 MBps (or 200 MBps for a loop based on 2 Gbps technology).
c) Switched Fabric Loop
It applies to switches and directors that support the FC-SW standard, that is, it is not limited to switches as its name suggests. A Fibre Channel fabric is one or more fabric switches in a single, sometimes extended, configuration. Switched fabrics provide full bandwidth per port compared to the shared bandwidth per port in arbitrated loop Implementations.
4. What’s the need for separate network for storage why LAN cannot be used?
LAN hardware and operating systems are geared to user traffic, and LANs are tuned for a fast user response to messaging requests. With a SAN, the storage units can be secured separately from the servers and totally apart from the user network enhancing storage access in data blocks (bulk data transfers), advantageous for server-less backups.
5. What is FCP?
The Fibre Channel Protocol (FCP) is the interface protocol of SCSI on Fibre Channel. It is a gigabit-speed network technology primarily used for Storage Networking. Fibre Channel is standardized in the T11 Technical Committee of the International Committee for Information Technology Standards (INCITS), an American National Standard Institute (ANSI) accredited standards committee. It started for use primarily in the supercomputer field but has become the standard connection type for storage area networks in enterprise storage. Despite its name, Fibre Channel signaling can run on both twisted-pair copper wire and fiber optic cables.
6. What is iSCSI?
- Internet SCSI (iSCSI) is a transport protocol that carries SCSI commands from an initiator to a target. It is a data storage networking protocol that transports standard Small Computer System Interface (SCSI) requests over the standard Transmission Control Protocol/Internet Protocol (TCP/IP) networking technology.
- iSCSI enables the implementation of IP-based storage area networks (SANs), enabling customers to use the same networking technologies — for both storage and data networks. As it uses TCP/IP, iSCSI is also well suited to run over almost any physical network. By eliminating the need for a second network technology just for storage, iSCSI has the potential to lower the costs of deploying networked storage.
7. What is FCIP?
Fibre Channel over IP (FCIP) is also known as Fibre Channel tunneling or storage tunneling. It is a method to allow the transmission of Fibre Channel information to be tunneled through the IP network. FCIP encapsulates Fibre Channel block data and subsequently transports it over a TCP socket. TCP/IP services are utilized to establish connectivity between remote SANs. Any congestion control and management, as well as data error and data loss recovery, is handled by TCP/IP services and does not affect FC fabric services. The major point with FCIP is that does not replace FC with IP, it simply allows deployments of FC fabrics using IP tunneling
8. What is iFCP
Internet Fibre Channel Protocol (iFCP) is a mechanism for transmitting data to and from Fibre Channel storage devices in a SAN, or on the Internet using TCP/IP. iFCP gives the ability to incorporate already existing SCSI and Fibre Channel networks into the Internet. iFCP is able to be used in tandem with existing Fibre Channel protocols, such as FCIP, or it can replace them. Whereas FCIP is a tunneled solution, iFCP is an FCP routed solution.iFCP is a gateway-to-gateway protocol and does not simply encapsulate FC block data. Gateway devices are used as the medium between the FC initiators and targets. As these gateways can either replace or be used in tandem with existing FC fabrics, iFCP could be used to help migration from a Fibre Channel SAN to an IP SAN or allow a combination of both
9. What is FICON?
FICON is a protocol that uses Fibre Channel as its physical medium. FICON channels are capable of data rates up to 200 MBps full duplex, they extend the channel distance (up to 100 km), increase the number of control unit images per link, increase the number of device addresses per control unit link, and retain the topology and switch management characteristics of ESCON.
10. What is the FICON address?
FICON generates the 24-bit FC port address field in yet another way. When communication is required from the FICON channel port to the FICON CU port, the FICON channel (using FC-SB-2 and FC-FS protocol information) will provide both the address of its port, the source port address identifier (S_ID), and the address of the CU port, the destination port address identifier (D_ID) when the communication is from the channel N_Port to the CU N_Port.
11. What is FSPF?
FSPF keeps track of the links on all switches in the fabric and associates a cost with each link. The cost is always calculated as being directly proportional to the number of hops. The protocol computes paths from a switch to all other switches in the fabric by adding the cost of all links traversed by the path and choosing the path that minimizes the cost.
12. How FSPF works
The collection of link states (including cost) of all switches in a fabric constitutes the topology database (or link state database). The topology database is kept in all switches in the fabric, and they are maintained and synchronized to each other. There are an initial database synchronization and an update mechanism.
82 Introduction to Storage Area Networks.T the initial database synchronization is used when a switch is initialized, or when an ISL comes up. The update mechanism is used when there is a link state change. This ensures consistency among all switches in the fabric.
13. What is Network Attached Storage (NAS)?
Network Attached Storage (NAS) is basically a LAN-attached file server that serves files using a network protocol such as the Network File System (NFS). NAS is a term 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 engine that implements the file services (using access protocols such as NFS or CIFS), and one or more devices, on which data is stored. NAS elements may be attached to any type of network. From a SAN perspective, a SAN-attached NAS engine is treated just like any other server, but a NAS does not provide any of the activities that a server in a server-centric system typically provides, such as e-mail, authentication, or file management.
14. How is Fiber Channel Different from ISCSI?
Fibre Channel and iSCSI each have a distinct place in the IT infrastructure as SAN alternatives to DAS. Fibre Channel generally provides high performance and high availability for business-critical applications, usually in the corporate data center. In contrast, iSCSI is generally used to provide SANs for business applications in smaller regional or departmental data centers.
15. What are the Frames?
Fibre Channel places a restriction on the length of the data field of a frame at 528 transmission words, which is 2112 bytes. (See Table 3-2 on page 52.) Larger amounts of data must be transmitted in several frames. This larger unit that consists of multiple frames is called a sequence. An entire transaction between two ports is made up of sequences administered by an even larger unit called an exchange.
A frame consists of the following elements:
- SOF delimiter
- Frame header
- Optional headers and payload (data field)
- CRC field
- EOF delimiter
16. What is Loop address?
An NL_Port, like a N_Port, has a 24-bit port address. If no switch connection exists, the two upper bytes of this port address are zeroes (x’00 00’) and referred to as a private loop. The devices on the loop have no connection with the outside world. If the loop is attached to the fabric and an NL_Port supports a fabric login, the upper two bytes are assigned a positive value by the switch. We call this mode a public loop.
17. What is LUN?
LUN unique number that is assigned to each storage device or partition of the storage that the storage can support
18. What is LUN Masking?
A method used to create an exclusive storage area and access control. And this can be achieved by the storage device control program.
19. What is WWN?
WWN is a 64bit address that is hard-coded into a fiber channel HBA and this is used to identify individual port (N_Port or F_Port) in the fabric.
20. What is metal?
A metal is a type of LUN whose maximum capacity can be the combined capacities of all the LUNs that compose it. The metaLUN feature lets you dynamically expand the capacity of a single LUN (base LUN) into a larger unit called a metaLUN. You do this by adding LUNs to the base LUN. You can also add LUNs to a metaLUN to further increase its capacity. Like a LUN, a metaLUN can belong to Storage Group and can participate in Snap View, Mirror View, and SAN copy sessions. MetaLUNs are supported only on CX-Series storage systems. A metaLUN may include multiple sets of LUNs and each set of LUNs is called a component. The LUNs within a component are striped together and are independent of other LUNs in the metaLUN.
21. What is an HBA?
Host bus adapters (HBAs) are needed to connect the server (host) to the storage.
22. What is SAN fabric?
SAN fabric is a hardware device that connects workstations and servers to storage devices in a SAN network. It uses the Fibre Channel switching technology to connect a server to a storage device. The SAN fabric offers a high-speed dedicated network including high availability features, very low latency, and high throughput.
23. 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.
24. 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 a single drive. This grouping enhances the performance of the logical drive beyond the physical capability of the drives.
25. What are the advantages of SAN?
- Massively extended scalability.
- Greatly enhanced device connectivity.
- Storage consolidation.
- LAN-free backup.
- Server-less (active-fabric) backup.
- Server clustering.
- Heterogeneous data sharing.
- Disaster recovery – Remote mirroring.
While answering people do NOT portray clearly what they mean & what advantages each of them has, which are cost-effective & which are to be used for the client’s requirements.
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26. What is the difference b/w SAN and NAS?
The basic difference between SAN and NAS, SAN is Fabric based and NAS is Ethernet based.
SAN – Storage Area Network
It accesses data on block level and produces space to host in the form of a disk.
NAS – Network-attached Storage
It accesses data on file level and produces space to host in the form of a shared network folder.
27. Can you briefly explain each of these Storage area components?
Fabric Switch: It’s a device which interconnects multiple network devices. There are switches starting from 16 port to 32 ports which connect 16 or 32 machine nodes etc. vendors who manufacture this kind of switches are Brocade, McData.
28. What is the most critical component in SAN?
Each component has its own criticality with respect to the business needs of a company.
29. How is a SAN managed?
There are many management software’s used for managing SAN’s to name a few:
- Centricity.
- IBM Tivoli Storage Manager.
- CA Unicenter.
- Veritas Volume manager.
30. 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.
31. 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. The highest priority of SCSI is ID 7 and the lowest ID is 8.
32. 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 through 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.
33. What is an Array?
An array is a group of Independent physical disks to configure any Volumes or RAID volumes.
34. Can you describe at-least 3 troubleshooting scenarios which you have come across in
detail?
SCENARIO 1: How do you find/debug when there is an 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.
Sometimes it is even hard to troubleshoot some of the things such as media errors in the
drives, or some of the drives taking a 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 the 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 the 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 the exact hardware type.
35. Which are the 4 types of SAN architecture types?
- Core-edge.
- Full-Mesh.
- Partial-Mesh.
- Cascade.
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36. Which command is used in Linux to know the driver version of any hardware device?
dmesg.
37. How many minimum drives are required to create R5 (RAID 5)?
You need to have at least 3 disk drives to create R5.
38. 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:
- Online.
- Degraded.
- Rebuilding.
- Failed.
39. What are the protocols used in physical/data link and network layer of SAN?
- Ethernet.
- SCSI.
- Fibre Channel.
40. What is storage virtualization?
Storage virtualization is an amalgamation of multiple n/w storage devices into a single storage unit.
41. 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).
42. What is virtualization?
Virtualization is the 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.
43. 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 to 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 App server ready to take over the operations. End customer never experiences any outage when there is an HA network infrastructure.
44. 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
the 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.
45. 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.
46. Name the features of SCSI-3 standard?
QAS: Quick arbitration and selection.
Domain Validation.
CRC: Cyclic redundancy check.
47. 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.
48. What is the disk array?
Set of high-performance storage disks that can store several terabytes of data. Single disk
the array can support multiple points of connection to the network.
49. What are different types of protocols used in transportation and session layers of SAN?
Fibre Channel Protocol (FCP).
Internet SCSI (iSCSI).
Fibre Channel IP (FCIP).
50. 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
51. What are the main constraints of SCSI in storage networking?
Deployment distance (max. of 25 pts).
The number of devices that can be interconnected (16).
52. What is Fabric?
Interconnection of Fibre Channel Switches.
53. What are the services provided by Fabric to all the nodes?
- Fabric Login.
- SNS.
- Fabric Address Notification.
- Registered state change notification.
- Broadcast Servers.
54. 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 fiber channel HBA and this is used to identify
individual port (N_Port or F_Port) in the fabric.
55. What are the different topologies in Fibre Channel?
- Point-to-Point.
- Arbitrary Loop.
- Switched Fabric Loop.
56. What are the layers of Fibre Channel Protocol?
- FC Physical Media.
- FC Encoder and Decoder.
- FC Framing and Flow control.
- FC Common Services.
- FC Upper-Level Protocol Mapping.
57. What is zoning?
Fabric management service that can be used to create logical subsets of devices within a
SAN. This enables the portioning of resources for management and access control purpose.
58. 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.
59. How does FC Switch maintain the addresses?
FC Switch uses a simple name server (SNS) to maintain the mapping table.
60. What are the two major classifications of zoning?
Two types of zoning are:
- Software Zoning.
- Hardware Zoning.
61. What are the different levels of zoning?
- Port-Level zoning.
- WWN Level zoning.
- Device Level zoning.
- Protocol Level zoning.
- LUN Level zoning.
62. What are the 3 prominent characteristics of SAS Protocol?
Native Command Queuing (NCQ.)
Port Multiplier.
Port Selector.
63. What are the 5 states of Arbitrary Loop in FC?
- Loop Initialization.
- Loop Monitoring.
- Loop arbitration.
- Open Loop.
- Closed Loop.
64. What is LUN Masking?
A method used to create an exclusive storage area and access control. And this can be
achieved by the storage device control program.
65. What is a snapshot?
A snapshot of data object contains an image of data at a particular point of time.
66. What is hot-swapping?
Devices are allowed to be removed and inserted into a system without turning off the system.