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EMC Interview Questions

What Is Lun Masking?

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.

What Is Lun, Logical Unit Number?

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.

What Is Wwn Zoning?

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.

Explain The Device Masking Architecture In Storage Arrays?

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).

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How To Calculate Rpms Of Ssd?

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

How Will You Calculate Iops Per Drive?

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

1000 / (Seek Time + Latency) = IOPS

 How to calculate HDD capacity?

Capacity = Heads X Cylinders X Sectors X Block Size

How will you calculate number of drives required?

Total Approximate Drives required = (RAID Group IOPS / (Hard Drive Type IOPS)) + Large Random I/O adjustment + Hot Spares + System Drives

If you know I/O load and IOPS, how will you calculate how many drives will be needed?

Total Approximate Drives = (RAID Group IOPS / (Hard Drive Type IOPS)) + Large Random I/O adjustment + Hot Spares + System Drives

How will you calculate HDD Capacity?

Capacity = Heads X Cylinders X Sectors X Block Size

With Active- Passive storage array what multipathing policy you will choose?

I will use Fixed, or Preferred, path management policy to intelligently segment workload across both controllers.

Tell us a generic method to provision SAN Storage from any Array?

1. Plan

2. Validation with Support Matrix for Host Connectivity

3. Provide Connectivity

4. Pick Volumes

5. Make Meta Volumes if necessary

6. Map out Zoning

7. Map to storage arrays Ports

8. Create Zones

9. LUN Mask

10. Discover on Server

How do you reserve the devices?

symconfigure -sid XXXX -f createdev.cmd -expire expiration date-owner myself -comment “this devices are reserved for SRDF activity” reserve

What is Buffer-to-Buffer Credits?

Buffer credits, also called buffer-to-buffer credits (BBC) are used as a flow control method by Fibre Channel technology and represent the number of frames a port can store. Fibre Channel interfaces use buffer credits to ensure all packets are delivered to their destination. Flow-control mechanism to ensure that Fibre Channel switches do not run out of buffers, so that switches do not drop frames .overall performance can be boosted by optimizing the buffer-to-buffer credit allotted to each port.

What is Drooping? How to check it?

Drooping= Bandwidth Inefficiency
Drooping begins if:  BB_Credit Where RTT = Round Trip Time
SF = Serialization delay for a data frame

How to calculate RPMs of SSD?

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

How will you calculate the required band width with write operations?

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.

How will you calculate Raw Capacity?

Raw Capacity= Usable + Parity

How do you check the free space by Disk group and Array as whole?

By Disk Group : Symdisk -sid XXXX list -by_diskgroup
Array as whole : Symconfigure -sid XXXX list -freespace

How do you check the total assigned devices to a particular Host?

Symmaskdb -sid XXXX list devs -wwn “host hba wwn”

How do you check the total allocated storage of a particular Host?

symmaskdb -sid XXXX list capacity -Host hostname

What Factors You Will Consider For Designing A San?

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:

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

What is Port Zoning?

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.

Why we need LUN Masking?

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.

How many LUN IDs available per FA port?

256 LUN IDs are available per FA port, 255 LUN IDs are usable out of 256.

What are the possible device service states and device status states?

Device Service States : Normal, Failed and Degraded

Device Status States : Ready, Not Ready and Write Disable.

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