EMC Interview Questions & Answers

Do you want to excel in computer field? Are you familiar with computer embedded systems? Wanted fetching and growth in your job? Then move on to wisdom jobs online portal and explore your career. EMC is an electromagnetic compatibility, the use of components in electronic system that do not electrically interfere with each other. EMC storage refers to various storage products, systems which are essential for virtualized and cloud computing environment. Candidates who are willing to join in EMC jobs have a wide scope in EMC design jobs, Embedded Developer jobs, embedded engineer jobs, embedded software developer jobs, EMC compliance testing jobs, EMC symmetric jobs and so on. So, grab the opportunity by looking at the EMC interview questions and answers framed below.

EMC Interview questions

EMC Interview Questions

  1. Question1. What Is Lun Masking?

    Answer :

    LUN (Logical Unit Number) Masking is an authorization process that makes a LUN available to some hosts and unavailable to other hosts.

    LUN Masking is implemented primarily at the HBA (Host Bus Adapter) level. LUN Masking implemented at this level is vulnerable to any attack that compromises the HBA. Some storage controllers also support LUN Masking.

  2. Question2. Why We Need Lun Masking?

    Answer :

    LUN Masking is important because Windows based servers attempt to write volume labels to all available LUN’s. This can render the LUN’s unusable by other operating systems and can result in data loss.

    Device masking lets you control your host HBA access to certain storage arrays devices. A device masking database, based in the storage arrays unit, eliminates conflicts through centralized monitoring and access records. Both HBA and storage arrays director ports in their Channel topology are uniquely identified by a 64-bit World Wide Name (WWN). For ease of use, you can associate an ASCII World Wide Name (AWWN) with each WWN.

  3. Question3. How Will You Ensure That San-attached Tape Devices Are Represented Consistently In A Host Operating System?

    Answer :

    • Use the Persistent Binding for Tape Devices.
    • Persistent binding is a host-centric enforced way of directing an operating system to assign certain SCSI target IDs and LUNs.
    • Persistent Name Binding support is for target devices.
    • Persistent binding is provided for users to associate a specified device World Wide Port Name (WWPN) to a specified SCSI target ID.
    • For example, where a specific host will always assign SCSI ID 3 to the first router it finds, and LUNs 0, 1, and 2 to the three-tape drives attached to the router.

    Practical examples:

    For Emulex HBA on a Solaris host for setting up persistent binding:

    # lputil
    MAIN MENU

    1. List Adapters
    2. Adapter Information
    3. Firmware Maintenance
    4. Reset Adapter
    5. Persistent Bindings

    Using option 5 will perform a manual persistent binding and the file is: /kernel/drv/lpfc.conf file.

    lpfc.conf file looks like:

    fcp-bind-WWNN=”50060XY484411 c6c11:lpfc0t1″,
    “50060XY4411 c6c12:lpfc1t2”;

    sd.conf file looks like:
    name=”sd” parent=”lpfc” target=1 lun=0;
    name=”sd” parent=”lpfc” target=2 lun=0;

    Reconfigure:

    # touch /reconfigure
    # shutdown -y -g0 -i6

  4. Question4. What Is Lun, Logical Unit Number?

    Answer :

    Logical Unit Number or LUN is a logical reference to entire physical disk, or a subset of a larger physical disk or disk volume or portion of a storage subsystem.

  5. Question5. What Is Wwn Zoning?

    Answer :

    WWN zoning uses name servers in the switches to either allow or block access to particular World Wide Names (WWNs) in the fabric. A major advantage of WWN zoning is the ability to recable the fabric without having to redo the zone information. WWN zoning is susceptible to unauthorized access, as the zone can be bypassed if an attacker is able to spoof the World Wide Name of an authorized HBA.

  6. Question6. What Is Port Zoning?

    Answer :

    Port zoning utilizes physical ports to define security zones. A user’s access to data is determined by what physical port he or she is connected to. With port zoning, zone information must be updated every time a user changes switch ports. In addition, port zoning does not allow zones to overlap. Port zoning is normally implemented using hard zoning, but could also be implemented using soft zoning.

  7. Question7. What Is The Difference Between Hard And Soft Zoning?

    Answer :

    • Hard zoning is zoning which is implemented in hardware.
    • Soft zoning is zoning which is implemented in software.
    • Hard zoning physically blocks access to a zone from any device outside of the zone.
    • Soft zoning uses filtering implemented in fibre channel switches to prevent ports from being seen from outside of their assigned zones. The security vulnerability in soft zoning is that the ports are still accessible if the user in another zone correctly guesses the fibre channel address.

  8. Question8. Explain The Device Masking Architecture In Storage Arrays?

    Answer :

    The device masking commands allow you to:

    Assign and mask access privileges of hosts and adapters

    Connected in a Fibre Channel topology to storage arrays and devices.

    Specify the host bus adapters (HBAs) through which a host can access storage arrays devices.

    Display or list device masking objects and their relationships: Typical objects are hosts, HBAs, storage arrays devices, and Fibre Channel Adapter (FA) ports.

    Modify properties, such as names and access privileges associated with device masking objects (for example, change the Name of a host).

  9. Question9. How Do You Know What Type Of Fibre Cable Is Needed?

    Answer :

    Select it on the basis of transmission distance.

    If the distance is less than a couple of miles, I will use multimode fibre cable.

    If the distance is more than 3-5 miles, I will use single mode fibre cable.

  10. Question10. How Will You Calculate Raw Capacity?

    Answer :

    Raw Capacity= Usable + Parity

  11. Question11. How Will You Calculate The Required Band Width With Write Operations?

    Answer :

    The required Bandwidth=the required bandwidth is determined by measuring the average number of write operations and the average size of write operations over a period of time.

  12. Question12. How To Calculate Rpms Of Ssd?

    Answer :

    SSD drives have no movable parts and therefore have no RPM.

  13. Question13. How Will You Calculate Iops Per Drive?

    Answer :

    To calculate IOPS per drive the formula I will use is:

    1000 / (Seek Time + Latency) = IOPS

  14. Question14. Can You Allocate A Lun Larger Than 2.19tb Limit Of Mbr ?

    Answer :

    Use GPT.

    GUID Partition Table, GPT is a part of the EFI standard that defines the layout of the partition table on a hard drive. GPT provides redundancy by writing the GPT header and partition table at the beginning of the disk and also at the end of the disk.

    GPT Uses 64-bit LBA for storing Sector numbers. GPT disk can theoretically support up to 2^64 LBAs. Assuming 512 byte sector emulation, maximum capacity of a GPT disk = 9.4 x 10^21 bytes = 9.4 zettabytes (ZB)

  15. Question15. Explain Your Experience With Disk Sparing?

    Answer :

    SAN Storage array has data integrity built into it.

    A storage  array uses spae disk drives to take the place of any disk drives that are blocked because of errors. Hot spares are available and will spare out predictively when a drive fails.

    There are two types of disk sparing:

    Dynamic Sparing: Data from the failed or blocked drive is copied directly to the new spare drive from the failing drive

    Correction Copy: Data is regenerated from the remaining good drives in the parity group. For RAID 6, RAID 5, and RAID 1, after a failed disk has been replaced, the data is copied back to its original location, and the spare disk is then available.

  16. Question16. What Factors You Will Consider For Designing A San?

    Answer :

    • ISL over Subscription Ratio
    • SAN Fan–in and Fan-Out
    • Storage Ports
    • Server I/O Profiles
    • Fabric Features
    • Continuity Requirements

    Design should address three separate levels:

    1. Tier 1: 99.999% availability (5 minutes of downtime per year)
    2. Tier 2: 99.9% availability (8.8 hours average downtime per year, 13.1 hours maximum)
    3. Tier 3: 99% availability (3.7 days of downtime per year)

  17. Question17. What Is Drooping? How To Check It?

    Answer :

    Drooping= Bandwidth Inefficiency

    Drooping begins if:  BB_Credit<RTT/SF

    Where RTT = Round Trip Time

    SF = Serialization delay for a data frame

  18. Question18. How Will You Decide How Many Storage Arrays Can Be Attached To A Single Host?

    Answer :

    use: Fan Out

    For example 10:1.

    I will determine this ratio, based on the server platform and performance requirement by consulting Storage vendors

  19. Question19. What Best Practices You Will Follow To Setup Isl Trunking?

    Answer :

    • I will directly connect participating switches byInter-Switch Link (ISL) cables.
    • I will keep the Trunk ports in the same port group
    • I will make sure Trunk ports run at the same speed
    • I will ensure that all Trunk ports are set to the same ISL mode (L0 is the default).
    • I will convert Trunk ports to be E_Ports or EX_Ports

  20. Question20. Which Load Balancing Policies Are Used Between Inter Switch Links? Explain With An Example?

    Answer :

    I have used Brocade SAN and it has these load balancing policies:

    • DLS – Dynamic Load Sharing. FSPF link balancing by FSPF routing protocol
    • DPS – Dynamic Path Selection by effectively striping IOs at SCSI level
    • Frame-level load balancing – Each successive frame on a different physical ISL.