Storage area networking Tutorial

Storage Types :

DAS : Direct Attached Storage : Server (or host)is directly connected to storage.


NAS : Network Attached Storage : NAS is essentially a file server which is connected to storage thru some network interface using widely supported IP protocols. NFS,CIFS are supported.


SAN : Storage Area Networking : Storage networks that connect multiple hosts through a switched fabric such as Fibre Channel or iSCSI.SAN is configured with multiple switches and multiple server Host Bus Adapters (HBA) to create a high-availability storage configuration and various RAID solutions are used to protect data at the disk level.


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Though many of Job hunters have good knowledge about DAS,NAS,SAN usually while answering some of the basic interview questions like

1. Differentiate between DAS-NAS-SAN
2. When NAS is a better option than DAS
3. When SAN is a better option than NAS
4. What are the advantages & disadvantages of each of these product types
(Above are Real Questions asked in a recent interview in one of the Storage test job interview)

Some more interview questions with brief answers

1. Name some of the SAN topologies
point-topoint,arbitrated loop, and switched fabric topologies

2. Whats the need for separate network for storage why LAN can not be used?
LAN hardware and operating systems are geared to user traffic, and LANs are tuned for a fast user response to messaging requests.
With a SAN, the storage units can be secured separately from the servers and totally apart from the user network enhancing storage access in data blocks(bulk data transfers), advantageuos for serverless backups.

3. What are the advantages of RAID ?
“Redundant Array of Inexpensive Disks”
Depending on how we configure the array, we can have the
- data mirrored [RAID 0] (duplicate copies on separate drives)
- striped [RAID 1] (interleaved across several drives), or
- parity protected [RAID 5](extra data written to identify errors).
These can be used in combination to delier the balance of performance and reliability that the user requires.


4. When JBOD's are used ?
“Just a Bunch of Disks”
It is a collection of disks that share a common connection to the server, but don’t include the mirroring,
striping, or parity facilities that RAID systems do, but these capabilities are available with host-based software.

5. Differentiate RAID & JBOD ?

RAID: “Redundant Array of Inexpensive Disks”
Fault-tolerant grouping of disks that server sees as a single disk volume
Combination of parity-checking, mirroring, striping
Self-contained, manageable unit of storage

JBOD: “Just a Bunch of Disks”
Drives independently attached to the I/O channel
Scaleable, but requires server to manage multiple volumes
Do not provide protection in case of drive failure

6. What is a HBA ?
Host bus adapters (HBAs) are needed to connect the server(host) to the storage.

SATA - Serial ATA Controllers Video Review


RAID (Redundant Array of Independendt Disks) Controller Review Video


7. What are the advantages of SAN ?

Massively extended scalability
Greatly enhanced device connectivity
Storage consolidation
LAN-free backup
Serverless (active-fabric) backup
Server clustering
Heterogeneous data sharing
Disaster recovery - Remote mirroring
While answering people do NOT portray clearly what they mean & what advantages each of them have, which are cost effective & which are to be used for the client's requirements.

Please focus on having your fundamentals STRONG & PERFECT.
Write to me roger.smithson@gmail.com to get more interview questions for storage jobs