Technical Interview Round for Storage & SAN Support engineer

I had to wait for nearly 40 minutes for the secound round of Technical interview. Read previous post (below post) Wipro Storage Interview to know what they asked in HR round.

There were very few guys in storage/SAN who came for this interview though it was a widely publicised walkin. There were more than 60 guys each for Software Testing, Java Development, Dotnet programming , Oracle ,Networking etc but for Storage hardly 5 guys came for the interview. This boosted my confidence - I was already imagining that I will definitely be given offer letter. Read the full posts to get all the details of this experience.

Second round was taken by two guys one seemed like a lead & another an engineer with little experience. Lead asked most of the questions & the new engineer asked twisted questions out of my own answers - it was more of a verification of my confidence in the subject.

Questions asked in that technical round of interview were like:
1. What kind of Storage Solutions have you worked on ?
2. Describe customer scenarios which you worked in & what problem did I resolve with my Storage knowledge ?
3. What Storage subsystems I have working experience on ?
4. Which vendor equipments I've used ?
5. How did you configure a SAN box from scratch ?
6. How do I plan , provision & manage Lun creation for different teams withing an organization ?
7. What are the difficulties I've faced in optimally utilizing the Storage infrastructure ?
8. What troubleshooting I've done & what are the steps I've followed ?
9. How different is it to manage a FC SAN & an iSCSI SAN ?
10.Mentioned some of the major company Storage products mention their specifications , limitations & performance comparisons ?
11. How will I manage if I have to work with Vmware Virtualization in my infrastructure do I have any exposure with ESX Server Administration or with Virtual Infrastructure management ?
12. What are the High Availability (HA) & Disaster Recovery Solutions (DR) I've implemented & how did I work out all the initial planning,designing,implementation & maintenance?
13. What is Zoning ? Mention types of Zoning & What Zoning options are available in which company products ?
14. What is Storage Virtualization & Storage Consolidation ?
15. Explain RAID5,RAID50,RAID10,RAID6,RAID3 which one is prefered & when ?

More details about how the interview went on will be posted in next 30 minutes keep reading .

Dont forget to see job openings for Storage in EMC2,HP,Wipro & many major companies in Storage Jobs Blog

For People who are interested to learn manual application Testing find real company Testing Interview Questions by clicking Testing Materials Website

Job Interview Questions with answers Real experiences of Storage Job Interviews

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Solaris Interview questions with answers for Storage professionals

31) How will you set a default router ?
A) # /etc/defaultrouter

32) How to remove all current routes and assign 192.168.1.100 as default router?
A) # route flush
# route add default 192.168.1.100

33) How to change the network settings ?
A) # sys-unconfig

34) What all does the NVRAM store?
A) Ethernet Address / Host ID / Time of Day (TOD) clock and EEPROM Parameters

35) Where are all the port numbers stored?
A) Port numbers are stored in /etc/services

36) Where are eeprom file stored ?
A) /usr/sbin/eeprom

37) Some important NIS commands :
1) # ypcat hosts à Prints info from hosts database
2) # ypmatch host1 hosts à Match individual host entries
3) # ypmatch user1 passwd
4) # ypwhich à Returns NIS master server.

38) Controlling the tape drive ?
1) mt –f /dev/rmt/0n à ‘n’ indicates no rewind.

39) What are the network utilities ?
1) snoop à To capture network packets & display contents
2) netstat –i à Displays state of Ethernet address
3) ndd command à Set & examine kernel parameters namely TCP/IP drivers.

40) Network Configuration :
1) /etc/resolv.conf : Contains Internet domain name, name server and search order.

2) /etc/nsswitch.conf : Specifies information source from files, NIS, NIS+ or DNS

3) /etc/hostname.[int](hme0|eri0|le0] : IP v4 host

4) /etc/nodename : IP v6 host

5) /etc/inet/hosts : Host namefile (/etc/host links to this file)

6) /etc/inet/netmasks : TCP/IP subnet router

7) /etc/inet/protocols : Network protocols

8) /etc/inet/services : Network service name & port numbers

9) /etc/notrouter : Create this file to prevent in.routed or in.rdiscd from starting at boot time

10) /etc/inet/inetd.conf : Internet super daemon config file

11) To change hostname / ip address :

/etc/hostname.{int}(hme0|le0)
/etc/nodename
/etc/inet/hosts
/etc/net/*/hosts
/etc/defaultrouter
/etc/resolv.conf


41) How to configure interfaces at boot time>
A) /etc/rcS.d/s30network.sh file à This script is run each time system is booted. It uses ifconfig utility to configure each interface with IP add & other network info.It searches for files called : hostname.xxn in /etc where xx à int type & nà instance of interface.

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Job roles and responsibilities in Storage IT industry

the kind of opportunities available for you in SAN industry

SAN Design and Deployment Engineer.
SAN Administrator.
SAN Applications developer.
SAN device driver and Firmware development engineer for different components such host controllers,Arrays,Switches.
SAN Support Engineer.
Backup and Recovery Administrators.
SAN testing engineers.

Find more information on Storage Area Network tutorials or SAN tutorials coming in this blog.

SAN Design & Deployment Engr : If you aspire to be a software architect & if you have the right skill for the same - this is a role you can fit into. Well this is something which needs atleast 1-2 years of SAN experience interms of actual hands on exposure in deployment of SAN infrastructure. ( We will include some Real Life implementation details & lots of graphics to help you understand this better )

SAN Administrator : Are you good in networking and system administration then there are loads of SAN administrator openings ( We will post the job requirements for each of these requirements in our future postings)

SAN Applications developer : If u r good in development of C/Unix or say any programming then you can very well fit into this role - U just need to have a good understanding of SAN fundamentals & very good programming skillset.

SAN device driver and Firmware development engineer for different components such host controllers,Arrays,Switches : All those embedded systems experts here is a golden opportunity for you - If you have good experience in device driver and Firmware development and though you are new to SAN you still are very much in demand . Yes you can get very good salary for your high skills.

SAN Support Engineer : Freshers here is a silver line for you - This is the most easiest way for a job hunter to get into SAN jobs. Yes it is not a high demanding job initially and it is not too tough and it is actually going to help you build your career. A support engineer in SAN is expected to have a fair SAN exposure ( YOu will get training once you join so dont worry :) . He is responsible to handle customer service requests & will be on call to resolve those technical issues and will build his expertise along the way - You get promotions and big pay as well .
No - This is not a call center kind of job. But this is far better interms of helping you learn as well as Earn in a technical environment.

Backup and Recovery Administrators : take any software industry they need a "Backup and Recovery Administrator" actually they need many. So this is also very much suited for freshers & new comers. We will go into details about this job requirement & how can a newcomer start his preparation to get a job in some similar roles. SAN Jobs are great for anyone to build their tech as well as domain knowledge.

SAN testing engineers: Testing Engineers in SAN this job is sooo much in demand that We are planning to have a detailed blogpost entirely on this subject. For time being - yes this is also very much suited for freshers/newcomers and compared to all other jobs this is an easy to get , easy to win the interviews kind of jobs. So u can get started in this segment if you are too lazy to work hard for other roles described above.

If You Like to See more such articles Plz add comments in this blog - also send a mail to roger.smithson@gmail.com - You will get a personalised training .

How will be a Company's Network Infrastructure

Continuing the trend of images find below some more real Company implementations of Storage,Network & Systems.

Two OBF servers sit on top of an SGI Altix

Digi Console Servers for remote configuration


Sunfire V20Z - AMD Opteron Based Servers from Sunmicrosystems

The servers site in a private 6ft x 8ft colocation cage. The datacenter itslf belongs to bostondatacenters.com -- an excellent facility

These 2 servers belong to the Open Bioinformatics Foundation, they host projects and sites such as bioperl.org, biojava,org, biodas.org, biomoby.org, biopython.org, bioruby.org, EMBOSS FTP

Rackable storage server (18x 250Gb SATA drives!) on top of an engineering prototype Intel system


Previous Posts on Storage Technology Jobs

How To Setup Storage Lab : Simple & Cheap

Motivated by Sarfaraz's comment for this blog asking for a post about Setting up a Scaled down(Home version/Cheap) Storage Lab,here is a an article on the same topic.

NAS ( Network Attached Storage)

Below is a Video of a simple NAS which you can build buying an old IDE hard disk drive along with some equipment like Vantec Nexstar LX NAS.
It looks like an external hard drive(USB based) but this same device can be connected thu Network cable & will actually become a simple NAS device.


FreeNAS.org - Below is a Video detailing how a NAS can be build using software from freenas.org & using an old PC with some hard disks. This video is quite interesting but the NAS topic starts somewhere in the middle - so be patient & its a huge video file.


BELOW IS THE MOST INTERESTING STORY
Skyers is more than happy to share the saga of building a FC SAN(Fibre Channel - Storage Area Network) at home. The SAN was entirely 1 gigabit per second (Gbps), and all the disks were SCSI(Small Computer System Interface). Skyers said he got most of the half-terabyte system in parts on eBay.

"It's actually funny how cheap these parts are," Skyers said; for example, his FC-connected SCSI array cost $22 on the online auction site. An old Compaq 1 Gbps FC card cost him $4. A newer QLogic FC card was more pricey, at $700, but the complete system, he said, including processors, memory, RAID controllers, and IDE and SATA disks -- tiered storage in the home -- set him back around $5,000.

"I guess I'm obsessive-compulsive in a way," he said. "I need to know as much about what I work with as possible. I can't take it apart and test the limits, much less break stuff, at work."

The initial push, he said, was to learn about FC signaling, how fast it can go, and how to get performance numbers from it. "I didn't want to just read the information off someone's marketing media," Skyers said.

One thing Skyers said he learned quickly about FC was that compatibility issues between different cards can be frustrating.

"They're both running the same protocol," Skyers said. "I don't get why one slightly newer card won't work with the older one."

Wrestling with the FC SAN -- contrasted with the rest of his Ethernet home network and the advent of new high-capacity NAS boxes like Buffalo Technology's new Drivestation Duo, which packs 1 TB of storage into a $500 product -- has made him convinced FC will soon be a thing of the past at work as well as at home. In the enterprise space, Skyers said, he compares Sun Microsystems Inc.'s "Thumper" 24 TB DAS array to the Buffalo box. "If I can have a subsystem in a box like that that's the size of something like Nexsan's ATABeast with about a gazillion drives, and I can hook it up to my IP switch, throw one in another place for disaster recovery (DR), what do I need a SAN for?" he said.

Meanwhile, Skyers said, his home experiments have only deepened his love for VMware, another key component, he said, in consolidating down into a box like Buffalo's. However, he said, through experimentation he has learned that VMware is "very picky" about installing on a SCSI drive in the physical host. "I tried a Linux trick to present a SATA and an IDE drive to it as a SCSI disk, but no dice," Skyers said.

What's next? DR and exploring the WAN -- echoing enterprise trends. "A cousin in Florida and I are going to set up separate islands of storage several hundred miles apart, and then see if we can replicate back and forth to them over low-bandwidth connections," Skyers said.

Frustration with data management -- at work and at home

Jeff Boles, IT manager for the City of Mesa, Ariz., says he thinks home storage is a "canary in the mine" for the enterprise. "What you see at home today will become active in the enterprise tomorrow."

Boles said he uses a NAS device and open-source software Debian for management. He boots the NAS device from a flash drive and mirrors it to another identical box. The clients that connect to it are a variety of laptops.

The problem he wrestles with, Boles said, is similar to one being articulated in the enterprise today -- data management and classification. Boles, an avid photographer, stores around 40 gigabytes (GB) of digital photos at any one time, as well as various versions of those photos that have been touched up. "There's a pressing need there to be able to correlate versions of the same file," he said. "There's really no good versioning system -- and it's made data proliferate. My biggest beef with storage in general, at work and at home, is the absurd gap between how data is structured and how it's physically stored."

Hope you have some idea now on how to setup ur own Storage lab - if anyone of u does some experiments plz do email me & I'll be happy to share with all our readers.

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Storage Basics Tutorial to help you prepare for Job Interview

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DEFINITIONS OF TERMS USED ALL THROUGHOUT THIS BLOG

A node is a computer attached to a SAN.
A SAN is a high-speed subnetwork of shared storage devices.
Software that manages San file system functions, such as file locking, space allocation, and data access authorization, is called the Metadata controller.(This is an Apple Storage implementation term - other companies use other terms)
Metadata controller uses callbacks to communicate with file system clients.

Xsan file system client software runs on all nodes in the SAN and communicates with the metadata controller in order to provide Xsan services. The term file system client refers to a node that is running the Xsan file system client software.

A redundant array of independent disks (RAID) device is a category of disk devices that combines two or more drives increased for fault tolerance and performance. There are several RAID levels:
*Level 0 provides data striping, where blocks of a file are spread across multiple disks, increasing performance; this level does not have any provisions that increase fault tolerance.
*Level 1 provides disk mirroring.
*Level 3 provides the data striping of Level 0 and also reserves a disk for storing error correction data, thereby increasing performance and fault tolerance.
*Level 5 provides data striping at the byte level and maintains stripe error correction information.

A JBOD (just a bunch of disks) is a disk that is not configured for RAID.

A logical unit number (LUN) is an aggregation of physical devices. Applications access LUNs through the special files in the system’s /dev/disk directory. For RAID devices, a LUN is typically a RAID-5 with three or more physical drives making up the LUN. For JBOD devices, one JBOD is one LUN.

A storage pool is a grouping of LUNs that have the same characteristics. Another term for storage pool is stripe group. One or more storage pools form a mountable volume. The number of volumes hosted by a single Xsan metadata controller should not exceed eight.

Stripe depth is the number of disks that have been assigned to a storage pool.

The stripe breadth is the maximum amount of data that is read or written before switching to the next LUN in the storage pool. When the last LUN is reached, I/O operations go back to t he first LUN. This is how large logical I/O operations are broken down into stripes across multiple LUNs. For example, if the stripe breadth for a storage pool is set at 4 MB, each I/O operation on that storage pool is physically no more than 4 MB. A 16 MB I/O operation would be broken down into 4 physical I/O operations.

A stripe line is the stripe breadth multiplied by the number of LUNs in the storage pool. To maximize performance, make I/O requests that area stripe line in size.

For real-time I/O, well-formed I/O is I/O that is a stripe line in size. This size makes the best utilization of the disks in the storage pool and maximizes the transfer rate. For non-real-time I/O, well-formed I/O is I/O that is memory aligned (modulus 4 bytes), 512-byte sector aligned, and modulus sector sized.

A block is the smallest number of bytes that can be read or written.

Storage pools can be assigned one or more values, known as an affinity identifiers, and a file can be assigned one affinity. When a request is made to allocate space in a file for which the affinity has been set, the space is allocated from the storage pool that an affinity identifier that matches the file’s affinity. For example, consider a SAN with some moderate performance JBOD LUNs and some high performance RAID-5 LUNs. By grouping the RAID-5 LUNs into the same storage pool and assigning them a specific affinity identifier, the developer can steer performance critical data to that storage pool. Files containing less critical data or files that do not have an affinity are assigned to the storage pool that consists of JBOD LUNs.

When a storage pool is in real-time I/O mode, file system clients that have processes that do non-real-time I/O must request a non-real-time I/O token Xsan throttles the speed of I/O of applications that are not in real-time mode so that their I/O does not interfere with real-time I/O. This document uses the term gate to describe processes or file descriptors that are not in real-time I/O mode and the term ungated to describe processes or file descriptors that are in real-time I/O mode.

An extent is a chunk of file data whose allocation is contiguous on a storage pool. A file’s data may be stored in one or more extents. Information about an extent includes its file-relative starting byte offset, its file system starting byte offset, the file system ending byte offset, and the ordinal of the storage pool on which the extent resides. File system clients use extent mapping tables to load information about a file’s extents. Loading extent information improves performance by eliminating a subsequent trip by the file system client to the metadata controller in order to retrieve extent information for the range mapped by an I/O request.

When there are two or more storage pools that have the same characteristics, an allocation strategy is needed. The strategy can be to round-robin files through the set of storage pools, balance the remaining space in the storage pools, or fill the first storage pool before going to the next storage pool.

A disk file system, such as a UFS or HFS+ file system, resides on the internal drives of a computer or on storage devices that are attached directly to the computer. A network file system allows data on internal drives or on directly attached drives to be shared with other computers on the network. Examples of network file systems include Apple Filing Protocol (AFP), Server Message Block (SMB), Common Internet File System (CIFS), or Network File System (NFS). A distributed file system is a blend of disk file system and network file system used to simplify data sharing through the creation of a single shared name space across a collection of servers. A cluster file system gives multiple computers simultaneous, very high-speed access to all shared data residing on an external, centralized storage pool. The storage pool typically consists of highly available RAID systems. Xsan is a cluster file system

SAN Architecture


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