Storage interview questions & answers for Series 1

We had 10 SAN interview questions in our earlier blogpost - Answers are given below

1) What is the differerence 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
NAS - Network attached Storage

2)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 buisenss following are essentials componets of SAN

- Fabric Switch
- FC Controllers
- JBOD's

3)Can you briefly explain each of these Storage area components?
Fabric Swictch: It's a device which interconnects multiple network devices .There are swithes 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.

FC Controllers : These are Data transfer medias they will sit on PCI slots of Server,u can configure Arrays and volumes on it.

JBOD: Just Bunch of Disks is Storage Box,it consists of Enclosure where set of harddrives are hosted in many combinations such SCSI drives,SAS ,FC,SATA.

4)What is the most critical component in SAN ?
Each component has its own criticality with respect to buisness needs of a company.

5) Define RAID ? Which one you feel is good choice ?

RAID (Redundant array of Independent Disks) is a technology to achive redundancy with faster I/O.There are Many Levels of RAID to meet different needs of the customer which are : R0,R1,R5,R10,R5.
Generally customer choose R5 to achive better redundancy and speed and it is cost effective.

6)How is a SAN managed ?

There are many management softwares used for managing SAN's to name a few

- Santricity
- IBM Tivoli Storage Manager.
- CA Unicenter.
- Veritas Volumemanger.

7) 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

8) 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 Conrollers,but most of the OS'es 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 installion 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.

9) What is Array ?

Array is a group of Independent physical disks to configure any Volumes or RAID volumes.

10)Can u describe atleast 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 trouble shoot some of the things such as media errors in the drives, or some of the drives taking long time to spinnup.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.