Q1 : What Are Multi-pathing Schemes And Which One To Use For Optimal Performance?
A : Servers/ hosts use multipathing for failover from one path to the other when one path from the Servers/host to the SAN becomes unavailable, the host switches to another path.
Servers/ hosts can also use multipathing for load balancing.
Types of policy:
Most Recently Used: The path used by a LUN is not be altered unless an event instructs the path to change. I will use this policy is for Active/Passive arrays and many pseudo-active/active arrays. Most recently used (mru) selects the path most recently used to send I/O to a device.
Fixed: The path used by a LUN is always the one marked as preferred unless that path is unavailable I use this policy is for Active/Active arrays. Fixed (fixed) uses only the active path.
Round Robin: Round robin (rr) uses the mru target selection policy and any HBA selection policy to select paths.
Custom (custom) sets the LUN to expect a custom policy.
Q2 : What is Drooping? How to check it?
A : Drooping= Bandwidth Inefficiency
Drooping begins if: BB_Credit Where RTT = Round Trip Time
SF = Serialization delay for a data frame
Q3 : Explain your experience with disk sparing?
A : SAN Storage array has data integrity built into it.
A storage array uses spare 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:
1. Dynamic Sparing: Data from the failed or blocked drive is copied directly to the new spare drive from the failing drive
2. 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.
Q4 : Explain how BB Credits and port speeds are related?
A : Number of Buffers: BB_Credit = [port speed] x [round trip time] / [frame size]
Q5 : How to calculate RPMs of SSD?
A : SSD drives have no movable parts and therefore have no RPM.
Q6 : How do you know what type of fiber cable is needed?
A : I select it on the basis of transmission distance.
If the distance is less than a couple of miles, I will use multimode fiber cable.
If the distance is more than 3-5 miles, I will use single mode fiber cable.
Q7 : What is the difference between Hard and Soft Zoning?
A : 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 fiber 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 fiber channel address.
Q8 : What is LUN, Logical Unit Number?
A : A Logical Unit Number or LUN is a logical reference to entire physical disk or a subset of a larger physical disk or disk volume or portion of a storage subsystem.
A : Raw Capacity= Usable + Parity
Q10 : Can you allocate a LUN larger than
A : 1. I will use GPT.
2. 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.
3. GPT Uses 64-bit LBA for storing Sector numbers. GPT disk can theoretically support up to 2^64 LBAs. Assuming
A : 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
Q12 : How will you calculate IOPS per drive?
A : To calculate IOPS per drive the formula I will use is:
1000 / (Seek Time + Latency) = IOPS
Q13 : What is WWN zoning?
A : 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 re-cable 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.
Q14 : What is LUN masking?
A : 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.
Q15 : Why we need LUN Masking?
A : 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.
Q16 : Have you used CLI to create Zones on a SAN switch?
A : Yes, on brocade:
1. I will create an alias.
aliCreate “aliname”, “member; member”
2. I will create a zone.
zonecreate “Zone Name”, “alias1; alias2″
3. I will add the zone to the defined configuration.
cfgadd “ConfigName”, “ZoneXYZ″
# cfgadd “configuration_Name”, “Zone_name”
4. I will save the defined configuration to persistent storage.
# cfgsave
5. I will enable the configuration.
cfgenable “ConfigName”
# cfgenable ” configuration_Name “
Q17 : What is Port Zoning?
A : 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.
Q18 : Explain the Device Masking Architecture in storage arrays?
A : The device masking commands allow you to:
1. Assign and mask access privileges of hosts and adapters
2. Connected in a Fibre Channel topology to storage arrays and devices.
3. Specify the host bus adapters (HBAs) through which a host can access storage arrays devices.
4. Display or list device masking objects and their relationships: Typical objects are hosts, HBAs, storage arrays devices, and Fibre Channel Adapter (FA) ports.
5. Modify properties, such as names and access privileges associated with device masking objects (for example, change the Name of a host).
Q19 : How can you see the Load on the open systems connected to SAN?
A : Platform Tool
AIX
Glance+
Linux
Windows Performance Monitor
Solaris
Vmware
Q20 : What are the Generic Method to Provision San Storage from a
A : Plan
Validation with Support Matrix for Host Connectivity
Provide Connectivity
Pick Volumes
Make Meta Volumes if necessary
Map out Zoning
Map to storage arrays Ports
Create Zones
LUN Mask
Discover on Server
Q21 : How will you calculate HDD Capacity?
A : Capacity = Heads X Cylinders X Sectors X Block Size
Q22 : What is relation between rotational speed and latency time?
A : The Rotational speed and latency time is related as follows:
Latency time = (1/((Rotational Speed in RPM)/60)) * 0.5 * 1000 milli seconds
Latency and RPM:
HDD
Spindle RPM Average rotational latency [ms]
7,200 4.17
10,000 3.00
15,000 2.00
Q23 : How will you calculate Max IOPS an HBA Port can generate to any LUN?
A : Max IOPS an HBA Port can generate to any LUN = (Device Queue Depth per LUN * (1 / (Storage Latency in ms/1000)))
Q24 : 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
Q25 : How Will You Decide How Many Storage Arrays Can Be Attached To A Single Host?
A : use: Fan Out
For example 10:1.
I will determine this ratio, based on the server platform and performance requirement by consulting Storage vendors