EMC Interview Questions and Answers
Last updated on 24th Oct 2020, Blog, Interview Question
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1. Network FailSafe device is controlled by which switch protocol?
2. Which NetWorker feature enables multiple storage nodes to use the same device?
Dynamic drive sharing
3. What value has the address space been increased to with the introduction of IPv6?
4. What is the role of a NetWorker storage node?
Manages backup devices
5. Which protocol is used by open systems hosts to access storage in Fiber Channel SANs?
6. A read cache miss operation on a Symmetrix has several steps. The first step is that the host sends a read request. What is the next step?
The Channel Director checks the track table.
7. What are two CLARiioN High Availability features?
Dual LCCs, Dual storage processor
8. What do VLANs reduce?
The number of packets processed by clients
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9. What does EtherChannel link aggregation do?
Disables links of a different speed to the majority of links in the trunk
10. What is used by NetWorker to manage its configuration?
11. In Asynchronous transmissions how are characters transmitted?
Single characters are transmitted at a time
12. What is UDP?
Connectionless base protocol
13. What are VDMs?
VDMs are isolated CIFS servers with their own environments
14. What generates the Content Address for a Centera?
15. Which level of backup is performed during a NetWorker consolidated backup?
16. In a NetWorker browsable recovery, what is true about the destination client?
Must also be the administering client
17. In a NetWorker recovery, which client role performs the recovery?
18. What is Celerra Replicator?
Is an asynchronous data replication solution
19. What is the default subnet mask for an IPv4 Class B address?
20. Which event occurs in a NetWorker server-initiated backup but NOT in a client-initiated backup?
Data life-cycle policies are enforced
21. How many octets in a default Class C IPv4 address make up the network portion?
22. Which NetWorker resource is used to determine the backup level for a client?
23. What is a characteristic of Centera?
Guaranteed content authenticity
24. What load balancing policies are available in PowerPath?
No Redirect, Round robin
25. Which of the following Symmetrix connectivity options can you use with Open Systems and Windows Hosts?
Fibre Channel and SCSI
26. Which of the following allows you to use ControlCenter Automated Resource Manager Storage Provisioning Services?
Storage pools and storage policies
27. In Celerra TimeFinder/FS Far Copy how does replication happen?
Source and Target are asynchronously replicated
28. In a Centera, what is a supported replication topology?
29. How many optical network ports are available on a NS500 DataMover?
30. What does the OSI Physical layer provide?
The media specification
31. What is a function of the API for Centera?
Separates the BLOB from the metadata
32. What is true about FTP and TFTP ?
FTP uses port 21 and TFTP uses port 69
33. When is Celerra SRDF used?
Is implemented over a campus distance
34. How is free maintained in the CLARIION write cache?
Cache is flushed to the driver during I/O only the least -recently used page are flushed
35. Which symmetric presents devices to hosts?
36. What does the control Center storage agent monitor?
37. When is the Port Bypass Card used on a Symmetrix DMX?
When the Disk Director fails
38. Which of the Celerra data replication options provides a point-in-time filesystem copy over IP?
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39. What does ISL aggregation do?
Enables distribution of traffic over the combined bandwidth of two or more ISLs and increases availability
40. What are features of Celerra Replicator?
Synchronous data recovery, Point-in-time copy over an IP network
41. Which protocol does open systems hosts use to access storage in Fibre Channel SANs?
42. Which NetWorker host performs the backup of the bootstrap save set?
Server during a server-initiated backup
43. Which product is used to create Logical Volumes on a Symmetrix system?
Control Center Symmetrix Manager
44. Which Symmetrix connectivity options can be used with mainframe hosts?
ESCON and FICON
45. Which control center view provides a single graphical view of the whole environment, including consolldated alters and threshold charts?
At A Glance
46. Which set component is required for write caching to be enabled in a CLARIION array?
2 power supplies, 2 storage processors,2 LCC cards and at least one standby power supply
47. What is a benefit of using zoning in a SAN?
Security at the switch port level
48. What is a characteristic of enterprise directors?
Fully redundant components
49. Which java based interface manages standalone MDS-Series switches?
50. Which protocol is used by open system hosts to access block level storage over IP?
51. What is a characteristic of a Content Address in Centera?
52. What is the use of Internet Control Message Protocol ICMP?
Sends administrative information between network devices
53. What is the purpose of storage groups in a CLARiiON storage array?
54. 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.
55. Why Do 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.
56. How Will You Ensure That San-attached Tape Devices Are Represented Consistently In A Host Operating System?
- 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.
For Emulex HBA on a Solaris host for setting up persistent binding:
- List Adapters
- Adapter Information
- Firmware Maintenance
- Reset Adapter
- 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;
- # touch /reconfigure
- # shutdown -y -g0 -i6
57. What Is Lun, Logical Unit Number?
Logical Unit Number or LUN is a logical reference to an entire physical disk, or a subset of a larger physical disk or disk volume or portion of a storage subsystem.
58. 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.
59. 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.
60. What Is The Difference Between Hard And Soft Zoning?
- 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.
61. 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).
62. How Do You Know What Type Of Fibre Cable Is Needed?
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.
63. How Will You Calculate Raw Capacity?
Raw Capacity= Usable + Parity
64. How Will You Calculate The Required Bandwidth 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.
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65. How To Calculate Rpms Of Ssd?
SSD drives have no movable parts and therefore have no RPM.
66. How Will You Calculate Iops Per Drive?
To calculate IOPS per drive the formula I will use is:
1000 / (Seek Time + Latency) = IOPS
67. Can You Allocate A Lun Larger Than 2.19tb Limit Of Mbr ?
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 disks 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)
68. Explain Your Experience With Disk Sparing?
SAN Storage array has data integrity built into it.
A storage array uses space 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.
69. What Factors You Will Consider For Designing A San?
- ISL overSubscription 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)
70. What Is Drooping? How To Check It?
Drooping= Bandwidth Inefficiency
Drooping begins if: BB_Credit<RTT/SF
Where RTT = Round Trip Time
SF = Serialization delay for a data frame
71. How Will You Decide How Many Storage Arrays Can Be Attached To A Single Host?
use: Fan Out
For example 10:1.
I will determine this ratio, based on the server platform and performance requirement by consulting Storage vendors
72. What Best Practices You Will Follow To Setup Isl Trunking?
- 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
73. Which Load Balancing Policies Are Used Between Inter Switch Links? Explain With An Example?
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.
74. How Will You Calculate Number Of Buffers Required?
Number of Buffers: BB_Credit = [port speed] x [round trip time] / [frame size]
75. What Are 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.
76. For Troubleshooting Have You Collected Logs From A San Switch?
Yes. I have been using Brocade Fabric and I have used “support save “to collect various logs for any issues.
- supportsave [ os | platform | l2 | l3 | custom | core | all ] <tftp server IP> <relative path> <user_tag>
77. How Will You Find Errors On Various Os Operating Systems To Troubleshoot Problems?
I will check the OS log files/event logs for errors:
- AIX: errpt -a
- Windows: event logs
- Solaris: /var/adm/messages
- linux: /var/log/messages
- HPUX: /var/adm/syslog/syslog.log
- Tru64: /var/adm/syslog
- SGI Irix: /var/adm/SYSLOG
- ESX: /var/log/vmkernel
- ESXi: /var/log/messages
78. How Will You Calculate Max Iops An Hba Port Can Generate To Any Lun?
Max IOPS an HBA Port can generate to any LUN = (Device Queue Depth per LUN * (1 / (Storage Latency in ms/1000)))
79. What Is Q-depth? How To Calculate It?
The queue depth is the maximum number of commands that can be queued on the system at the same time.
80. As a SAN administrator how will you tell your boss how many drives are required for a requirement?
I will use the formula:
Total Approximate Drives required = (RAID Group IOPS / (Hard Drive Type IOPS)) + Large Random I/O adjustment + Hot Spares + System Drives
81. How to calculate HDD capacity?
Capacity = Heads AND Cylinders AND Sectors X Block Size
82. You need to provision SAN storage with a certain IOPS. How will you find what kind of disks you need?
Input/output operations per second (IOPS) is the measure of how many input/output operations a storage device can complete within one second.
IOPS is important for transaction-based applications.
IOPS performance is heavily dependent on the number and type of disk drives.
To calculate IOPS of a Hard disk drive:
IOPS = —————————————
(Average Latency) + (Average Seek Time)
To calculate IOPS in a RAID:
(Total Workload IOPS * Percentage of workload that is read operations) + (Total Workload IOPS * Percentage of workload that is read operations * RAID IO Penalty)
83. How will you calculate the number of drives required?
Total Approximate Drives required = (RAID Group IOPS / (Hard Drive Type IOPS)) + Large Random I/O adjustment + Hot Spares + System Drives
84. 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
85. How will you calculate HDD Capacity?
Capacity = Heads AND Cylinders AND Sectors X Block Size
86. What is the relation between rotational speed and latency time?
The Rotational speed and latency time is related as follows:
Latency time = (1/((Rotational Speed in RPM)/60)) * 0.5 * 1000 milliseconds
Latency and RPM:
Spindle RPM Average rotational latency [ms]
87. With Active- Passive storage array what multipathing policy will you choose?
I will use Fixed, or Preferred, path management policy to intelligently segment workload across both controllers.
88. Tell us a generic method to provision SAN Storage from any Array?
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
89. How will you discover SAN disks on Hosts?
Disk Management console, Diskmgmt.msc
Rescan the devices:
- # /usr/sbin/ioscan -C disk
- ioscan – scan the I/O system
- driver | class] instance] hw_path] | [devfile]
- driver | class] instance] hw_path] [devfile]
- driver | class] instance] lun hw_path] [devfile]
- Generate device files: insf –e
- Verify the new devices: ioscan funC
Rescan the devices: cfgmgr vl fcsx, x is FC adapter number
Verify the new devices: lsdev Cc
- echo scsi add-single-device > /proc/scsi/scsi
Determine the FC channels: cfgadm -al
Force rescan: cfgadm o force_update c configure cx
Where x is the FC channel number
Force rescan at HBA port level: luxadm e forcelip /dev/fc/fpx
Force rescan on all FC devices: cfgadm al o show_FCP_dev
Install device files: devfsadm
Display all ports: luxadm e port
Display HBA port information luxadm -v display
Display HBA port information: luxadm e dump_map
To force Fibre Channel SAN disk rescan, Use device path from luxadm -e port output.
# luxadm -e forcelip
Sign in to VMware Infrastructure Client. Select the ESX host and then click the “Configuration” tab. Select “Storage Adapters” from under Hardware. Click “Rescan”
ESXESXi 4.x and before
ESXi 5.x and later
esxcli storage core adapter rescan –all
90. How will you get the WWN of all your HBAs to provision SAN storage?
- lscfg –v –l fcs#
- (fcs – FC Adapter)
- fcmsutil /dev/td#
- (td – Tachyon Adapter)
- emulex cfg –emc or
I can use Storage Explorer to see detailed information about the Fibre Channel host bus adapters (HBAs).
- Also I can use:
- more /var/adm/messages | grep –i wwn |more dmesg
5. VMware vSphere ESX/ESXi host
There are several ways to get HBA WWNs on VM
- vSphere Client;
- Using ESXi Shell;
- Using Powershell / PowerCLI script.
- /sys/class/scsi_host/hostN/device/fc_host/hostN/port_nameWhere “N” is the number of device for your fibre HBAs
91. What best practices will you follow to set up ISL Trunking?
1. I will directly connect participating switches byInter-Switch Link (ISL) cables.
2. I will keep the Trunk ports in the same port group
3. I will make sure Trunk ports run at the same speed
4. I will ensure that all Trunk ports are set to the same ISL mode (L0 is the default).
5. I will convert Trunk ports to be E_Ports or EX_Ports
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