EMC Clariion Interview Questions

Explain Clariion architecture?
The CLARiiON storage system is based on a modular architecture. The first building block of the architecture is the Disk Processor Enclosure, or DPE. The DPE houses the storage Processor(s) and the first Fibre Channel Arbitrated Loop (FC-AL) disks. Disk Array Enclosures (DAEs) are interconnected using Link Control Cards (LCCs).The module architecture allows the customer to add drives as needed to meet capacity requirements. When more capacity is required, additional disk array enclosures (DAE or DAE2) containing disk modules can be easily added. LCC or Link Control Cards are used to connect shelves of disks. In addition, the LCC monitors the FRUs within the shelf and reports status information to the storage processor. The LCC contains bypass circuitry that allows continued operation of the loop in the event of port failure.

Newer CLARiiON arrays have two processors per Storage Processor, and do not use a DPE. Instead, it utilizes an SPE or Storage Processor Enclosure. The SPE does not contain any disk modules, so it must have at least one DAE2 and a maximum of 16 DAE2s. CLARiiON Architecture is based on intelligent Storage Processors that manage physical drives on the back end and service host requests on the front end, be it Fibre Channel or iSCSI protocols. Storage Processors communicate to each other over the CLARiiON Messaging Interface (CMI). Both the front-end connection to the host and the back-end connection to the physical storage is 2Gb Fibre channel.

What are different types of Clariion models?
CX-200,300,300i,400,500,500i,600 and 700
CX3-10, 20, 40 and CX3-80
CX4-120, 240, 480 and CX4-960
AX Series
FC Series

What are the management tools for Clariion?
NaviSphere Manager
EMC Control Center

Minimum number of disks required to create RAID 1/0 raid group?

What is Access Logix?
Access Logix provides LUN masking that allows sharing of storage system.

What are the significant features of Access Logix?
LUN masking.
Presents a virtual storage system.
Maps CLARiiON LUNs (FLARE LUNs) to host LUNs.
Manages the Access Control List.
Manages Initiator Registration Records - Access Logix database entries.

Why Access Logix has to be enabled?
If Access Logix is not enabled all LUNs are presented to all storage system ports. Any host that connects to the storage system will then have access to all of the LUNs on that storage system. In environments where multiple hosts attach to the storage system, this will cause problems. Windows systems may attempt to take ownership of LUNs belonging to other Windows systems, and Unix systems may try to mount Windows LUNs, Access Logix solves these problems by performing LUN masking – it masks certain LUNs from hosts that are not authorized to see them, and presents those LUNs only to the server(s) which are authorized to see them. In effect, it present a ‘virtual storage system’ to each host – the host sees the equivalent of a storage system dedicated to it alone, with only its own LUNs visible to it.

Another task which Access Logix performs is the mapping of CLARiiON LUNs, often called FLARE LUNs or FLUs, to host LUNs. It will determine which physical addresses, in this case the device numbers, each attached host will use for its LUNs. Note that this feature is configurable by the user through the CLI and the GUI. Access to LUNs is controlled by information stored in the Access Logix database, which is resident in a reserved area of CLARiiON disk - the PSM LUN. The Access Logix software manages this database.When host agents in the CLARiiON environment start up, typically shortly after host boot time, they send initiator information to all storage systems they are connected to. This initiator information is stored in the Access Logix database.

How can you check and enable Access Logix?
Right click on Clariion Array select Properties from the drop down menu.
Click on Storage Access Tab
Check whether Access Control Enabled
How many initiators can be connected per port in CX500 CX600?
CX500 – 64 Initiators/Port
CX600 – 32 Initiators/Port

What is CMI? Clariion Message Interface?
Storage Processors communicate to each other over the CLARiiON Messaging Interface (CMI).

What is SP Collects and how do you gather SP Collects?
Spcollect is a Storage Processor based perl script which gathers significant information from the Storage Processor and bundles this information for investigation by engineering.

navicli –h {ip} spcollect {eng mode password} – invoke the spcollects

navicli –h {ip} managefiles –list – to monitor the progress

navicli –h {ip} managefiles –retrieve –file {filename} – to transfer spcollect file to management host.

The managefiles command will transfer the data file to the Navisphere CLI directory where the command was invoked.

Explain step by step procedure to assign a LUN to existing Host?
Will check is there any free space is available in existing RAID group as per the required LUN Capacity.

If not available create the new RAID group

Bind the LUN

Will go to the host’s storage group properties and open the LUN tab and add the newly created LUN

Explain step by step procedure for storage provision to the new host?
Installing HBA drivers in new host
Installing NaviAgent
Installing Powerpath if required
Creating Zone, add new zone to zone set, save and enable the zone.
Checking the host connectivity status in the array
Create a new RAID
Bind a LUN (create LUNs as per the host requirement)
Create a metaLUN if required
Create a Storage Group
Add Host and LUN in the storage group properties window
Reboot the host and check the LUN visibility at host-end.

What are pre requisites for LUN migration?
Migration moves data from one LUN to another LUN
Any RAID type to any RAID type, FC to ATA or ATA to FC
Neither LUN may be private LUNs or Hot Spares
Neither LUN may be binding, expanding, or migrating
Either or both may be metaLUNs
Destination LUN may not be in a Stora ge Group
Destination LUN may not be part of SnapView or MirrorView operations
Destination LUN may be larger than Source LUN

How do you create a Meta LUN?
Right Click on LUN > Select Expand > Expand Storage Wizard will appear click on Next > Select the Expansion Type (Stripped or Concatenate) and Click on Next > Confirm the Preserve Data dialog > Select the members (LUN) of Meta and click on Next > Select the User Capacity and click on Next > give the MetaLUN name, Default Owner, Expansion Rate, etc.. and click on Next > Review the Summary and click on Finish.

What is the recommended ration of Read and Write cache?
80% Read and 20% Write Cache

How do you troubleshoot if the Hosts are not registering issue?
1. Right click on clariion array and check the connectivity status whether the initiators are showing. If it is showing check whether the initiators are logged in.

2. If it is showing under connectivity status and registered status showing "NO" then you need to install Agent or else you need to register it manually.

3. If it is Registered and not logged in then you need to check the Zoning side and physical connectivity.

4. if the host initiators are not showing under connectivity status at all then you need check the zoning and physical connectivity. If possible remove the zone and create it back. Once you create the zone dont forget to Enable and Save the config. After this just refresh it.

5. Once all these tasks are fine then you can login to Navisphere and update the array once. Update is over then you can go to connectivity status and check.

What are the significant features of MetaLUN?
A metaLUN is created by combining LUNs
Dynamically increase LUN capacity
Can be done on-line while host I/O is in progress
A LUN can be expanded to create a metaLUN and a metaLUN can be further
Expanded by adding additional LUNs
Striped or concatenated
Data is restriped when a striped metaLUN is created
Appears to host as a single LUN
Added to storage group like any other LUN
Can be used with MirrorView, SnapView, or SAN Copy
Supported only on CX family with Navisphere 6.5+

What are the significant features of FLARE operating systems?
FLARE Operating Environment runs in the CLARiiON Storage Processor. I/O handling, RAID algorithms.
End-to-end data protection.
Cache implementation.
Provisioning and resource allocation.
Memory budgets for caching and for snap sessions, mirrors, clones, copies.
Process Scheduling.
Boot Management.

What are the significant features of Cache Memory?
Cache memory on an SP performs two tasks:
Staging: Temporary buffering of current read and write data.
Always performed on each I/O.
Storage: Repository for frequently accessed data.
Maintaining copies of read and write data.
User must explicitly enable this (for both read and write).

Burst Smoothing - Absorb bursts of writes without becoming “disk bound”.
Write cache optimization.
Locality - Merge several writes to the same area into a single operation.
Increases write performance.
Immediacy - Satisfy user requests without going to the disks.
Read cache optimization prefetching of data for sequential reads. 

What are the significant features of Clariion Event Monitor?
The Event Monitor GUI is integrated with Navisphere Manager.
Event Monitor is part of the Navisphere Agent.
Monitors for user-configurable events.
Reports those events in user-configurable ways.
May launch other utilities/applications.
Can send SNMP traps to Enterprise Management Platforms.

What are the Clariion Operating Layers?
EMC Control Center/ Clariion Based Applications
Navisphere Manager/NaviCli
FLARE Operating Environment
Clariion Hardware

Explain step by step procedure for LUN migration?
Right Click on the LUN and select migrate from the drop down menu.
Select the migration rate and click on OK.
We can check the status from migration tab in the LUN properties page.

What is the process of LUN Migration Operations?
Data is copied from Source LUN to Destination LUN
- Source stays online and accepts I/O

Destination assumes identity of Source when copy completes
- Storage Group membership

Source LUN is unbound after copy completes

The migration process is non-disruptive
– There may be a performance impact
LUN Migration may be cancelled at any point
- Storage system returns to its previous state

What is Private LUN?
The LUN becomes private LUN when you add it to the reserved LUN pool. Since the LUNs in the reserved LUN pool are private LUNs, they cannot belong to storage groups and a server cannot perform I/O to them.

What is Reserved LUN Pool?
The reserved LUN pool works with replication software, such as SnapView, SAN Copy, and MirrorView/A to store data or information required to complete a replication task. The reserved LUN pool consists of one or more private LUNs.

How do you create a user and assign access rights?
Click on Tools > Click on Security > Click on User management
From the User Management windows Click on Add
Give the user name, Role, access level (Global or Local) and password. 

How do you monitor Clariion alerts?
Using Clariion Event Monitor

How the Clariion Event Monitor works?
The Event Monitor GUI is integrated with Manager
Event Monitor is part of the Navisphere Agent
Event Monitor is designed to run in the background, without permanent supervision by the operator
Once Event Monitor is initially configured, there is no further need to run UI
Event Monitor relies on the text file navimon.cfg
Self-documenting text file included in Interface Kit
Does not require Event Monitor UI
Monitor Agents run on one or more hosts (or SPs) and watch over the storage systems
When an event is detected, the agent notifies the user As defined by navimon.cfg
Can send SNMP traps to Enterprise Management Platforms.

What are Vault drives and how much capacity they use?
Clariion Platform_____:Vault Drivers____:Vault overhead per drive

CX____________________:0-4______________:6.22 GB
CX3___________________:0-4______________:33 GB
CX4___________________:0-4______________:62 GB
AX4-5_________________:0-3______________:17.4 GB

Vault Drives:

All Clariions have Vault Drives. They are the first five (5) disks in all Clariions. Disks 0_0_0 through 0_0_4. The Vault drives on the Clariion are going to contain some internal information that is pre-configured before you start putting data on the Clariion. Vault Drives contains Vault area, PSM Lun, Flare database Lun and Operating System.

The Vault:

The vault is a ‘save area’ across the first five disks to store write cache from the Storage Processors in the event of a Power Failure to the Clariion, or a Storage Processor Failure.

The PSM Lun:

The Persistent Storage Manager Lun stores the configuration of the Clariion. Such as Disks, Raid Groups, Luns, Access Logix information, SnapView configuration, MirrorView and SanCopy configuration as well.

Flare Database LUN:

The Flare Database LUN will contain the Flare Code that is running on the Clariion. I like to say that it is the application that runs on the Storage Processors that allows the SPs to create the Raid Groups, Bind the LUNs, setup Access Logix, SnapView, MirrorView, SanCopy, etc…

Operating System:

The Operating System of the Storage Processors is stored to the first five drives of the Clariion.

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