1. WHAT ARE THE
BENEFITS OF FIBRE CHANNEL SANS?
Fibre Channel SANs
are the de facto standard for storage networking in the corporate data center
because they provide exceptional reliability, scalability, consolidation, and
performance. Fibre Channel SANs provide significant advantages over
direct-attached storage through improved storage utilization, higher data
availability, reduced management costs, and highly scalable capacity and
performance.
2. WHAT ENVIRONMENT
IS MOST SUITABLE FOR FIBRE CHANNEL SANS?
Typically, Fibre Channel SANs are most suitable for large
data centers running business-critical data, as well as applications that
require high-bandwidth performance such as medical imaging, streaming media,
and large databases. Fibre Channel SAN solutions can easily scale to meet the
most demanding performance and availability requirements.
3. WHAT CUSTOMER
PROBLEMS DO FIBRE CHANNEL SANS SOLVE?
The increased performance of Fibre Channel enables a highly
effective backup and recovery approach, including LAN-free and server-free
backup models. The result is a faster, more scalable, and more reliable backup
and recovery solution. By providing flexible connectivity options and resource
sharing, Fibre Channel SANs also greatly reduce the number of physical devices
and disparate systems that must be purchased and managed, which can
dramatically lower capital expenditures. Heterogeneous SAN management provides
a single point of control for all devices on the SAN, lowering costs and
freeing personnel to do other tasks.
4. HOW LONG HAS FIBRE
CHANNEL BEEN AROUND?
Development started in 1988, ANSI standard approval occurred
in 1994, and large deployments began in 1998. Fibre Channel is a mature, safe,
and widely deployed solution for high-speed (1 GB, 2 GB, 4 GB) communications
and is the foundation for the majority of SAN installations throughout the
world.
5. WHAT IS THE FUTURE
OF FIBRE CHANNEL SANS?
Fibre Channel is a well-established, widely deployed
technology with a proven track record and a very large installed base,
particularly in high-performance, business-critical data center environments.
Fibre Channel SANs continue to grow and will be enhanced for a long time to
come. The reduced costs of Fibre Channel components, the availability of SAN
kits, and the next generation of Fibre Channel (4 GB) are helping to fuel that
growth. In addition, the Fibre Channel roadmap includes plans to double
performance every three years
6. WHAT ARE THE
BENEFITS OF 4GB FIBRE CHANNEL?
Benefits include twice the performance with little or no
price increase, investment protection with backward compatibility to 2 GB,
higher reliability due to fewer SAN components (switch and HBA ports) required,
and the ability to replicate, back up, and restore data more quickly. 4 GB
Fibre Channel systems are ideally suited for applications that need to quickly
transfer large amounts of data such as remote replication across a SAN,
streaming video on demand, modeling and rendering, and large databases. 4 GB
technology is shipping today.
7. HOW IS FIBRE
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.
8. WHEN SHOULD I
DEPLOY FIBRE CHANNEL INSTEAD OF ISCSI?
For environments consisting of high-end servers that require
high bandwidth or data center environments with business-critical data, Fibre
Channel is a better fit than iSCSI. For environments consisting of many
midrange or low-end servers, an IP SAN solution often delivers the most
appropriate price/performance.
9. Name some of the
SAN topologies
Point-to-point,
arbitrated loop, and switched fabric topologies
10. 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.
11. What are the
advantages of RAID?
“Redundant Array of Inexpensive Disks”
Depending on how we configure the array, we can have the
- data mirrored [RAID 1] (duplicate copies on separate
drives)
- striped [RAID 0] (interleaved across several drives), or
- parity protected [RAID 5](extra data written to identify
errors).
These can be used in combination to deliver the balance of
performance and reliability that the user requires.
12. Define RAID?
Which one you feel is good choice?
RAID (Redundant array of Independent Disks) is a technology
to achieve redundancy with faster I/O. There are Many Levels of RAID to meet
different needs of the customer which are: R0, R1, R3, R4, R5, R10, R6.
Generally customer chooses R5 to achieve better redundancy
and speed and it is cost effective.
R0 – Striped set
without parity/[Non-Redundant Array].
Provides improved performance and additional storage but no
fault tolerance. Any disk failure destroys the array, which becomes more likely
with more disks in the array. A single disk failure destroys the entire array
because when data is written to a RAID 0 drive, the data is broken into
fragments. The number of fragments is dictated by the number of disks in the
drive. The fragments are written to their respective disks simultaneously on
the same sector. This allows smaller sections of the entire chunk of data to be
read off the drive in parallel, giving this type of arrangement huge bandwidth.
RAID 0 does not implement error checking so any error is unrecoverable. More
disks in the array means higher bandwidth, but greater risk of data loss
R1 - Mirrored set
without parity.
Provides fault tolerance from disk errors and failure of all
but one of the drives. Increased read performance occurs when using a
multi-threaded operating system that supports split seeks, very small
performance reduction when writing. Array continues to operate so long as at
least one drive is functioning. Using RAID 1 with a separate controller for
each disk is sometimes called duplexing.
R3 - Striped set with
dedicated parity/Bit interleaved parity.
This mechanism provides an improved performance and fault
tolerance similar to RAID 5, but with a dedicated parity disk rather than
rotated parity stripes. The single parity disk is a bottle-neck for writing
since every write requires updating the parity data. One minor benefit is the
dedicated parity disk allows the parity drive to fail and operation will
continue without parity or performance penalty.
R4 - Block level
parity.
Identical to RAID 3, but does block-level striping instead
of byte-level striping. In this setup, files can be distributed between
multiple disks. Each disk operates independently which allows I/O requests to
be performed in parallel, though data transfer speeds can suffer due to the
type of parity. The error detection is achieved through dedicated parity and is
stored in a separate, single disk unit.
R5 - Striped set with
distributed parity.
Distributed parity requires all drives but one to be present
to operate; drive failure requires replacement, but the array is not destroyed
by a single drive failure. Upon drive failure, any subsequent reads can be
calculated from the distributed parity such that the drive failure is masked
from the end user. The array will have data loss in the event of a second drive
failure and is vulnerable until the data that was on the failed drive is
rebuilt onto a replacement drive.
R6 - Striped set with
dual distributed Parity.
Provides fault tolerance from two drive failures; array
continues to operate with up to two failed drives. This makes larger RAID
groups more practical, especially for high availability systems. This becomes
increasingly important because large-capacity drives lengthen the time needed
to recover from the failure of a single drive. Single parity RAID levels are
vulnerable to data loss until the failed drive is rebuilt: the larger the
drive, the longer the rebuild will take. Dual parity gives time to rebuild the
array without the data being at risk if one drive, but no more, fails before
the rebuild is complete.
13. What is the
difference between RAID 0+1 and RAID 1+0
RAID 0+1 (Mirrored
Stripped)
In this RAID level all the data is saved on stripped volumes
which are in turn mirrored, so any disk failure saves the data loss but it
makes whole stripe unavailable. The key difference from RAID 1+0 is that RAID
0+1 creates a second striped set to mirror a primary striped set. The array
continues to operate with one or more drives failed in the same mirror set, but
if drives fail on both sides of the mirror the data on the RAID system is lost.
In this RAID level if one disk is failed full mirror is marked as inactive and
data is saved only one stripped volume.
RAID 1+0 (Stripped
Mirrored)
In this RAID level all the data is saved on mirrored volumes
which are in turn stripped, so any disk failure saves data loss. The key
difference from RAID 0+1 is that RAID 1+0 creates a striped set from a series
of mirrored drives. In a failed disk situation RAID 1+0 performs better because
all the remaining disks continue to be used. The array can sustain multiple
drive losses so long as no mirror loses both its drives.
This RAID level is most preferred for high performance and
high data protection because rebuilding of RAID 1+0 is less time consuming in
comparison to RAID 0+1.
14. When JBOD's are
used?
“Just a Bunch of Disks”
It is a collection of disks that share a common connection
to the server, but don’t include the mirroring,
striping, or parity facilities that RAID systems do, but
these capabilities are available with host-based software.
15. Differentiate
RAID & JBOD?
RAID: “Redundant Array of Inexpensive Disks”
Fault-tolerant grouping of disks that server sees as a
single disk volume
Combination of parity-checking, mirroring, striping
Self-contained, manageable unit of storage
JBOD: “Just a Bunch of Disks”
Drives independently attached to the I/O channel
Scalable, but requires server to manage multiple volumes
Do not provide protection in case of drive failure
16. What is a HBA?
Host bus adapters (HBAs) are needed to connect the server
(host) to the storage.
17. 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 have, which are cost effective & which
are to be used for the client's requirements.
18. 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 form of disk.
NAS - Network attached Storage
It accesses data on file level and produces space to host in
form of shared network folder.
19. What is a typical
storage area network consists of - if we consider it for implementation in a
small business setup?
If we consider any small business following are essentials
components of SAN
- Fabric Switch
- FC Controllers
- JBOD's
20. 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 these kind of
switches are Brocade, McData.
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.
46. 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)
47. What is a Fabric?
Interconnection of Fibre Channel Switches
48. 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
49. 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.
50. What are the
different topologies in Fibre Channel?
a) Point-to-Point
b) Arbitrary Loop
c) Switched Fabric Loop
51. 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
52. 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.
53. What are the two
major classification of zoning?
Two types of zoning are
a) Software Zoning
b) Hardware Zoning
54. 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
55. What are the 3
prominent characteristics of SAS Protocol?
a) Native Command
Queuing (NCQ)
b) Port Multiplier
c) Port Selector
56. 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
57. How does FC
Switch maintain the addresses?
FC Switch uses simple name server (SNS) to maintain the
mapping table
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. 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.
60. 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.
61. 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.
62. 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.
63. 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.
64. 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.
65. What is the
smallest unit of information transfer in FC?
Frame
66. How is the
capacity of the HDD calculated?
Number of Heads X Number of Cylinders X Sectors per track X
Sector Size
67. 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).
68. What are two
types of recording techniques on the tapes?
a) Linear Recording
b) Helical Scan Recording.
69. What is snapshot?
A snapshot of data object contains an image of data at a
particular point of time.
70. What is HSM?
Hierarchical storage management - An application that
attempts to match the priority of data with the cost of storage.
71. What is
hot-swapping?
Devices are allowed to be removed and inserted into a system
without turning off the system.
72. What is
Hot-Sparing?
A spare device is available to be inserted into the
subsystem operation without having to remove and replace a device.
73. What are
different types of backup system?
a) Offline
b) Online
c) Near Line
74. 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
75. Name few types of
Tape storage?
a) Digital Linear
Tape
b) Advanced Intelligent Tape
c) Linear Tape Open
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).
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.
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.
By हरिवंशराय बच्चन
