Advanced SAN interview Q&A

1.WHAT IS TIERED STORAGE?

It is a storage networking method where data is stored on various types of media based on performance, availability and recovery requirements. Today's tiered storage infrastructures range from simple two-tier architecture consisting of SCSI or fiber channel attached disk and tape to more complex infrastructures, which in some cases are comprised of five-to-six tiers.
In a single enclosure, we can have SSD, FC & SATA drives. Tiering across the storage is also possible.

  
Tier-one = Mission critical data. High performance & frequently accessed data.

Tier-two = Moderately used data and non.MC data.

Tier-three = High capacity drives with more data which are least accessed.
 
If the data in Tier-3 is used once, it is moved to Tier-1, to SSD drives.

For the next few days, if the accessibility is more, it stays in Tier-1.

If it is not used for few days, it goes to Tier-2 & later on to Tier-3. 
Tier1 = Solid state drive
Tier2 = FC or SAS
Tier3 = SATA or SAS with less rpm

 2. WHAT IS THIN PROVISIONING? 
Thin provisioning is the act of using virtualization technology to give the appearance of having more physical resources than are actually available.

In traditional allocation, storage space is allocated beyond current needs, (over-allocation)

While, TP relies on, on-demand allocation of blocks of data

Here is an example of Thick & Thin Provisioning, with simple everyday scenario.

Let us take an example of normal storage allocation, as shown in the picture above.

John & Peter need 5GB space for their project work. So the storage admin has allocated accordingly.

John = Volume-A of 5 GB

Peter = Volume-B of 5 GB.

Days pass by, and they successfully completed their project, But both of them used just 3 GB of space per volume.

The remaining 4 GB is unused and the admin cannot assign those volumes to anyone else, resulting is wastage of space.

Now, we will see how the space is saved using TP.

Let’s take the same example. This time, the Admin has thin LUNs & allocating just 1GB of space to each.

And the remaining space, he is allocating as “Available” storage. As per John & Peter, they can see 5 GB allocated in their system.

After they cross 1 GB, which the admin has allocated, the LUN grows! (it can grow upto 5GB)

After the completion of project in 3 months, they have used 3 GB each, and the remaining space is in “Available Storage” or “Pool”

Later on, the Admin can assign the remaining space to any other user.

After 80% usage of the Pool, the Admin gets a warning. In such scenario, he should consider expanding the array by adding more enclosures & disks.

Thick provisioning is typically more efficient when the amount of resource used is very close to the amount of resource allocated. Thin provisioning is more efficient where the amount of resource used is much smaller than allocated so that the benefit of providing only the resource needed exceeds the cost of the virtualization technology used.

EMC calls it as "virtual Provisioning".

http://wikibon.org/wiki/v/Analyzing_thin_provisioning_requirements

The above link shows how TP plays a role in business performance & in a company's revenue.

 3. EXPLAIN FAST TRACK TECHNOLOGY.
Fast Track technology enhances Automated Tiered Storage by dynamically placing the most frequently accessed data on the fastest, or outer, tracks of each drive. Meanwhile, the least active blocks of data remain on the inner tracks of all drives in each storage tier. The result is ready access to frequently used data with fewer drives than conventional enterprise network storage systems. 
This technology was introduced by DELL. (Applicable only for spinning drives)

 Architectural advantages:

• Use up to 30 percent fewer drives without sacrificing performance
• Reduce seek times for the most active blocks of data within each storage tier
• Reduce power consumption on costly, high-power drives
• Radically reduce the cost of storage.
• Improve the performance of every drive
• Operates inside the volume to improve performance
• Leverage Thin Provisioning to write only actual data to the fastest tracks of each drive
• Purchase fewer drives overall and efficiently utilize lower-cost drives – all without sacrificing performance!!

 4. EXPLAIN FCIP IN DETAIL WITH IT'S ADVANTAGES & LIMITATIONS.
FCIP=Fiber channel over IP
It's basically FC+IP, which connects 2 islands of FC SAN, to form a unified storage area network in a single Fibre Channel fabric.
The FC End Nodes are unaware of the existence of the FCIP Link.

 

FCIP encapsulates Fibre Channel and transports it over a TCP socket. FCIP is considered a tunneling protocol, as it makes a transparent point-to-point connection between geographically separated SANs over IP networks. FCIP relies on TCP/IP services to establish connectivity between remote SANs over LANs, MANs, or WANs. TCP/IP is also responsible for congestion control and management, as well as for data error and data loss recovery. 
Advantage:
An advantage of FCIP is that it can use TCP/IP as the transport while keeping Fibre Channel fabric services intact.  
Limitations:
FC Primitive Signals, Primitive Sequences, and Class 1 FC Frames are not transmitted across an FCIP Link because they cannot be encoded using FC Frame Encapsulation.


5. EXPLAIN iFCP IN DETAIL.
iFCP=Internet Fibre Channel Protocol.
iFCP maps to the OSI session layer.
It is a gateway-to-gateway protocol, which enables the implementation of fibre channel fabric functionality on an IP network in which IP components and technology replace the fibre channel switching and routing infrastructure.

The main function of the iFCP protocol layer is to transport fibre channel frame images between locally and remotely attached N_PORTs. When transporting frames to a remote N_PORT, the iFCP layer encapsulates and routes the fibre channel frames via a predetermined TCP connection for transport across the IP network. It is for bulk data transfer over internet. 
When receiving fibre channel frame images from the IP network, the iFCP layer de-encapsulates and delivers each frame to the appropriate N_PORT. The iFCP layer processes the following types of traffic:

1. FC-4 frame images associated with a fibre channel application protocol.
2.  FC-2 frames comprising fibre channel link service requests and responses
3. Fibre channel broadcast frames
4. iFCP control messages required to setup, manage or terminate an iFCP session.

6.WHAT IS THE DIFFERENCE BETWEEN iSCSI & iFCP.
iSCSI can be deployed without iSNS, wherein in iFCP requires iSNS.
in iFCP, a new service iSNS was created to provide the functionality of FC Network services & FC zone server.
 
7.WHAT IS THE ORIGINAL iFCP DESIGN CONCEPT & HOW WAS IT MODIFIED TO MEET THE DEPLOYMENT PRACTICE?
Below pictures explain the original design & the latest deployment design.
Original Design:



Current deployment Practice:



If the end nodes were attached via IP/Ethernet, the cost would be lower, but the solution would closely resemble iSCSI. Another challenge for iFCP is that only one vendor produces iFCP gateways today, and its iFCP products do not currently provide sufficient FC port densities to accommodate the connectivity requirements of most modern FC-SANs. So, iFCP gateways are usually deployed in conjunction with FC switches.