Know EMC FLARE Operating Environment.

FLARE software manages all functions of the CLARiiON storage system. Each storage system ships with a complete copy of FLARE software installed. When you power up the storage system, each SP boots and executes FLARE software.Access Logix software is optional software that runs within the FLARE operating environment on each storage processor (SP). Access Logix provides access control and allows multiple hosts to share the storage system. This “LUN Masking” functionality is implemented using Storage Groups. A Storage Group is one or more LUNs within a storage system that are reserved for one or more hosts and are inaccessible to other hosts. When you power up the storage system, each SP boots and executes its Access Logix software. Navisphere Management software is a suite of tools that allows centralized management of CLARiiON storage systems. Navisphere provides a centralized tool to monitor, configure, and analyze performance. CLARiiON can also be managed as part of EMC ControlCenter, allowing full end-to-end management.

Salient Features:-

1) FLARE Operating Environment runs in the CLARiiON Storage Processor.

– I/O handling, RAID algorithms.

– End-to-end data protection.

– Cache implementation.

2) Access Logix provides LUN masking that allows sharing of storage system.

3) Navisphere middleware provides common interface for managing CLARiiON.

4) CLARiiON optional software including

– Access Logix.

– MirrorView, SnapView, SAN Copy.

5) EMC ControlCenter provides end-to-end management of a CLARiiON.

6) FLARE performs provisioning and resource allocation.

7) Memory budgets for caching and for snap sessions, mirrors, clones, copies.

8) Process Scheduling.

9) Boot Management.

What is a Storage Processor ?

The main component in all CLARiiON series arrays is the Storage Processor. Storage Processors (SPs) are configured in pairs for maximum availability and are Field Replaceable Units (FRUs). SPs provide both front-end connectivity to the hosts and back-end connectivity to the physical disks. Each Storage Processor also includes up to 4 GB of memory, most of which is used for cache. Cache memory is segmented into read cache memory and write cache memory. Read cache memory is used for staging and prefetching read requests from the host. Write cache is used to accelerate host writes to the storage system. 

With write cache enabled, writes are mirrored to the write cache memory in the other storage processor over the CLARiiON Messaging Interface (CMI). The CMI is a Fibre Channel based link and operates at either 100MB/sec on FC series or 200MB/sec on CX series systems. Each storage processor also includes a TCP/IP connection that is used for configuration and management of the storage system.Each storage system ships with a complete copy of FLARE software installed on the first four disks on back-end loop 0. Disks 0_0 and 0_2 store mirrored copies of the software for SP A, and disks 0_1 and 0_3 store mirrored copies of the software for SP B. When you power up the storage system, each SP boots and executes FLARE software.

Salient Features :-

# Storage processors are configured in pairs for maximum availability.

# One or two processors per Storage Processor board.

# Two or four Fibre Channel front-end ports for host connectivity

– 1Gb or 2Gb.

– Arbitrated loop or switched fabric.

# Dual-ported Fibre Channel Disk drives at the back-end.

– Two or Four Arbitrated Loop connections.

# Maximum of 4GB of memory per SP.

– Write Cache is mirrored between Storage Processors for availability using the CMI 

(CLARiiON Messaging Interface)

– Write Caching accelerates host writes.

# Ethernet connection for management.

An Introduction To Clariion Architecture.

The CLARiiON storage system is based on a modular architecture. The concept is “buy and build as you go”. 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. Some older CX series arrays use the DPE2 which includes, in addition to the storage Processors, up to 15 2Gb dual-ported FC drives. Newer CX series, namely the CX300, CX500, and CX 700 can use a DAE2P, which provide for better fault isolation and reliability on the back end (BE) loops. The FC series DPE contains up to 10 1Gb dual-ported FC drives. In order to expand the capacity of the storage system, 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. Depending on the module, each Storage processor includes either one or two CPUs. 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 is a metaLUN in EMC Clariion ?

A metaLUN is created by combining 2 or more LUN's.MetaLUNs are supported only on CX-Series storage systems.The metaLUN feature lets you dynamically expand the capacity of a single LUN (base LUN) into a larger unit called a metaLUN. You do this by adding LUNs to the base LUN. You can also add LUNs to a metaLUN to further increase its capacity. Like a LUN, a metaLUN can belong to a Storage Group, and can participate in SnapView, MirrorView and SAN Copy sessions.During the expansion process, the host is able to process I/O to the LUN or metaLUN and access any existing data on the Base LUN. It does not, however, have access to any added capacity until the expansion is complete. Depending on the operating system, a reboot of the host or the use of a disk expansion utility, such as diskpar in Windows, may be used to claim the additional space. Each set of striped LUNs is called a component. All metaLUNs contain at least one component which includes the base LUN and one or more LUNs. Any data that gets written to a metaLUN component is striped across all the LUNs in the component. You can expand a LUN or metaLUN in two ways — stripe expansion or concatenate expansion. A stripe expansion takes the existing data on the LUN or metaLUN, and restripes (redistributes) it across the existing LUNs and the new LUNs you are adding.The stripe expansion may take a long time to complete and will affect performance while the expansion is in process . A concatenate expansion creates a new metaLUN component that includes the new LUNs and appends this component to the end of the existing LUN or metaLUN. There is no restriping of data between the original storage and the new LUNs. The concatenate operation completes immediately.

Salient Features :- 

# 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+

Fibre Channnel FC SAN Fabric Overview.

A fabric is a logically defined space in which Fibre Channel nodes can communicate with each other. A fabric can be created using just a single switch, or a group of switches connected together. The primary function of the fabric is to receive FC data frames from a source port (device) and route them to the destination port (device) whose address identifier is specified in the FC frames. Each port (device) is physically attached through a link to the fabric. Many models of switches can participate in only a single fabric. Some newer switches have the capability to participate simultaneously in multiple fabrics. Within a fabric, each participating switch must have a unique identifier called its Domain ID. A SAN provides two primary capabilities: block-level storage connectivity from a host to a storage frame or array, and block-level storage connectivity between storage frames or arrays.

In a Fibre Channel SAN, block requests are handled by a Fibre Channel HBA or Host-Based Adapter. A Fibre Channel HBA is a standard PCI or Sbus peripheral card on the host computer, just like a SCSI adapter. For most typical SAN installations, Fabric connect via switches (FC-SW) is the appropriate choice of Fibre Channel topology. Unlike a loop configuration, a switched fabric provides scalability, and dedicated bandwidth between any given pair of inter-connected devices. FC-SW uses a 24-bit address (called the Fibre Channel Address) to route traffic, and can accommodate as many as 15 million devices in a single fabric. Adding or removing devices in a switched fabric does not affect ongoing traffic between other unrelated devices.

An Overview on EMC IP SANs Architecture.

Nowadays iSCSI is becoming popular in the new generation Storage Area Networks. Unlike Fibre Channel SANs, IP SANs use the iSCSI protocol over standard IP networks for host-to-storage communications. iSCSI is also becoming an increasingly popular mechanism to bridge disparate SAN islands and fabrics into a single large fabric. These advantages allow companies to leverage their existing investment in IP technologies to grow their Storage networks. In an IP SAN, hosts communicate with Storage Arrays using Serial SCSI-3 over IP. Gigabit Ethernet (GigE) is a commonly used medium for connectivity. This eliminates the need for a Fibre Channel HBA on the host. Modern server-class hosts typically ship with two network ports (NICs) in their factory configuration, with at least one port being GigE-capable. So no extra hardware may be needed on the host for iSCSI connectivity.

A network entity is a device (a client, server or gateway) that is connected to an IP network. It contains one or more network portals. A network portal is a component within a network entity that is responsible for the TCP/IP protocol stack. Network portals consist of an initiator portal that is identified by its IP address, and a target portal that is identified by its IP address and listening port. An initiator makes a connection to the target at the specified port, creating an iSCSI session. An iSCSI initiator or target identified by its iSCSI address is known as an iSCSI node. A portal group is a set of network portals that support an iSCSI session that is made up of multiple connections over different network portals. iSCSI supports multiple TCP connections within a session. Each session can be across multiple network portals. Similar to DNS in the IP world, iSNS acts like a query database in the iSCSI world. iSCSI initiators can query the iSNS and discover iSCSI targets.

Some Interview Questions on SAN which are most regularly asked !!!!

1. What is power path?
2. Power path CLI to manage disks
3. List power path policy
4. What is vault drive?
5. What is the PSM LUN?
6. Basic of Storage
7. Define RAID? Which one you feel is good choice?
8. Storage array used in DAS
9. Explain iSCSI login, fabric login
10. Advantage of migration from DAS to SAN
11. What is Meta Lun?
12. Explain Clarion architecture
13. Explain DMX Architecture
14. Explain Enginuity operation layers
15. What is hard and soft zoning?
16. Explain WWN
17. What is zoning and how to create?
18. What is VSAN and how to create?
19. Hardware models of Clarion
20. What is FCID?
21. Explain Navisphere / Symmtric Management console / ECC
22. Initialization of clarion array
23. Explain rule 17 in DMX
24. Why and how symmask, symid and symcfg are used in DMX?
25. Symdev
26. Explain about symcfg
27. What is SYMAPI?
28. Configuration change in DMX
29. What is VCMDB?
30. Can windows, Linux, Solaris share the same FA in DMX?
31. What is Snap view?
32. What is mirror view?
33. What is SAN Copy?
34. Explain Time finder and SRDF
35. Difference in iSCSI and NAS
36. What is IQN?
37. Explain SAN, NAS and CAS using devices used in these model
38. Difference in iFCP and FCIP
39. What is fabric?
40. What is RAID? Explain RAID3, RAID5 and RAID 1/0
41. What is Hot Spare Disk?
42. What are the bay in DMX-3
43. Version and model
44. Brief the symmetrix CLI command
45. Create storage group and add device into storage group in DMX.
46. Create Time Finder clone using Cli
47. Composite Device group
48. Create SRDF
49. What is iSCSI?
50. What is Disk Controller?
51. How does data got saved in case of stripping and incase of concatenation?
52. What is the minimum no. of disks required for RAID 5 and RAID 6?
53. Difference between time finder and clone?
54. What is SRDF R1 & R2?
55. What is the version of Symmetrix DMX4?
56. In 4-24 what do 24 mean?
57. What is fabric?
58. Importance of RAID6?
59. How many disk Failures RAID5 supports?
60. Importance of masking?
61. Different RAID Levels?
62. What is quorum disk and its importance?
63. How to manually restore failed paths in Clarion?
64. Flash drives in DMX4
65. What is LCC? Link control card
66. Storage provisioning in DMX?
67. Steps for zoning using CLI?
68. Describe SMCLI commands you have used
69. LUN, Base LUN and MetaLun?
70. Difference between HP EVA 5000 and 8000?
71. What is CMI? Clariion message interface
72. What are the I/O operations in clariion?
73. Use of SPs?
74. What is VMCDB?
75. What is Hyper?
76. What is device in DMX?
77. What is SAN kit?
78. Channel directors and disk directors?
79. What is global memory?
80. Difference between Emulex and Qlogic?
81. What is storage array in Clariion?
82. What is FCID?
83. What is F-LOGI and P-LOGI? How authentication happens?