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MirrorView/Asynchronous (MirrorView/A) remote mirroring feature lets you periodically update a remote copy of production data. It is a software application that keeps a point-in-time copy of a logical unit (LUN) and periodically replicates the copy to a separate location in order to provide disaster recovery, that is, to let one image continue to be active if a serious accident or natural disaster disables the other. It provides data replication over long distances (hundreds to thousands of miles). To provide for disaster recovery, the primary and secondary storage systems should be geographically separated. MirrorView/A ensures that data from the primary storage system replicates to the secondary.

You can quickly restore operations when a catastrophic event, such as a fire, destroys the storage media at the primary data center. By mirroring critical data to a remote site, you not only retain vital data but can also quickly restore operations by switching over to the secondary storage system.

A remote mirror consists of a primary image and one secondary image . The production image (the one mirrored) is called the primary image; the copy image is called the secondary image. MirrorView/A supports one remote image per primary. The primary image receives I/O from a server called the production server; a separate storage system maintains the secondary image. This storage system can optionally have a failover/standby computer connected to it or can be connected to its own computer system. Both storage systems can be in different domains, which you manage with the User Interface (UI). The client that is managing the storage system containing the primary images can fail over to the secondary image if the primary image becomes inaccessible. After initial synchronization, the remote site always has a consistent point-in-time copy of the primary data.

You can perform the following tasks with remote mirroring:
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Create and destroy remote mirrors.
Add a secondary image to and remove a secondary image from a remote mirror.
Promote, synchronize, and fracture secondary mirror images.
View and modify all supported properties for remote mirrors.
View and modify all supported properties for primary and secondary mirror images.


Maximum remote asynchronous mirrors
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You can configure a maximum of 25 primary and secondary images on CX3 model 10 systems, 50 primary and secondary images on CX400, CX500, and CX3 model 20 systems and a maximum of 100 primary and secondary images on CX600, CX700, CX3 model 40 systems, and CX3 model 80 systems. The total number of primary and secondary images on the storage system make up this maximum number.

Introduction to RAID Groups
A RAID Group is a set of disks with a RAID type on which you bind one or more LUNs. The RAID Group supports the RAID type of the first LUN you bind on it, and any other LUNs you bind on it have that RAID type. The LUN is distributed equally across all the disks in the RAID Group

When you bind a LUN in a RAID Group, you specify how much of the Group’s available user space you want the LUN to use. For example, a RAID Group of RAID 5 type with five 9 Gbyte disks provides 36 Gbytes of user space and 9 Gbytes of parity data. If you bind one 2 Gbyte LUN, you will have 34 Gbytes left for additional LUNs. You could bind 17 more 2 Gbyte LUNs using all the space in the RAID Group or you could bind four more 2 Gbytes LUNs and four 5 GBbyte LUNs leaving 6 Gbytes for future expansion.

The number of disks you can have in a RAID Group depends on the Group’s RAID type. The following restrictions apply to RAID Groups and the LUNs on them:

128 LUNs maximum per RAID 6, RAID 5, RAID 3, RAID 1/0, RAID 1, DISK or RAID 0 Group.
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Note For RAID 3 And Disk RAID Groups, we strongly recommend 1 LUN maximum

1 LUN maximum per Hot Spare RAID Group

LUNs have the same RAID type as their RAID Group

Each LUN in a RAID Group can have a different element size where applicable

Different SPs can own different LUNs in the same RAID Group

When a disk in a RAID Group is replaced or fails, the rebuild operation reconstructs the data on the replacement disk or hot spare one LUN at a time starting with the first LUN.

A metaLUN is a type of LUN whose maximum capacity can be the combined capacities of all the LUNs that compose it. 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. MetaLUNs are supported on CX3-series and CX-Series storage systems.

A metaLUN may include multiple sets of LUNs and each set of LUNs is called a component. The LUNs within a component are striped together and are independent of other LUNs in the metaLUN. Any data that is written to a metaLUN component is striped across all the LUNs in the component. The first component of any metaLUN always includes the base LUN.

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 you are expanding, 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. A concatenate expansion creates a new metaLUN component that includes the new expansion LUNs, and appends this component to the existing LUN or metaLUN as a single, separate, striped component. No restriping of data between the original storage and the new LUNs occurs. The concatenate operation completes immediately.

Right click on the Storage array and choose create Raid group. While creating mention the no. of disks to be part of the Raid Group.

The raid type of the first LUN created in the RG will be the raid type for the RG. i.e. you can create luns which are of same raid type.

1. We need to create / identify an existing RAID group before creating the LUN. Though we don't specify the raid type while creating the raid group, it is necessary that we know the raid type of the new lun as the 'number of disks' in the raid group should be applicable for the raid type we need. For example if we choose 2 disks to be part of the new raid group then we cannot create a RAID 5 LUN in this as RAID 5 needs a minimum of 3 disks.

2. Once the RG is created, right click on it and choose create LUN.

3. Mention the capacity and RG while creating this.

4. Map the LUN using the storage group.

SAN Zoning in details!!!!!!!!!

Lets discuss about most important thing in SAN environment ZONING. Zoning is the only way to restrict access for storage to all the host. We will be discussing about Zoning in details.

There are two type of Zoning basically : Hard Zoning and Soft Zoning. Lets first define what is Zoning??

Zoning is nothing but map of host to device to device connectivity is overlaid on the storage networking fabric, reducing the risk of unauthorized access.Zoning supports the grouping of hosts, switches, and storage on the SAN, limiting access between members of one zone and resources in another.

Zoning also restricts the damage from unintentional errors that can corrupt storage allocations or destabilize the network. For example, if a Microsoft Windows server is mistakenly connected to a fabric dedicated to UNIX applications, the Windows server will write header information to each visible LUN, corrupting the storage for the UNIX servers. Similarly, Fibre Channel register state change notifications (RSCN) that keep SAN entities apprised of configuration changes, can
sometimes destabilize the fabric. Under certain circumstances, an RSCN storm will overwhelm a
switch’s ability to process configuration changes, affecting SAN performance and availability for
all users. Zoning can limit RSCN messages to the zone affected by the change, improving overall
SAN availability.

By segregating the SAN, zoning protects applications against data corruption, accidental access,
and instability. However, zoning has several drawbacks that constrain large-scale consolidated
infrastructures.

Lets first discuss what are type of Zoning and pro and cos:

As I have mentioned earlier that Zoning got two types basically you can say three but only 2 types popular in industry.

1) Soft Zoning 2) Hard Zoning 3) Broadcast Zoning

Soft Zoning : Soft zoning uses the name server to enforce zoning. The World Wide Name (WWN) of the elements enforces the configuration policy.
Pros:
- Administrators can move devices to different switch ports without manually reconfiguring
zoning. This is major flexibility to administrator. You don't need to change once you create zone set for particular device connected on switch. You create a zone set on switch and allocate storage to host. You can change any port for device connectivity

Cons:
- Devices might be able to spoof the WWN and access otherwise restricted resources.
- Device WWN changes, such as the installation of a new Host Bus Adapter (HBA) card, require
policy modifications.
- Because the switch does not control data transfers, it cannot prevent incompatible HBA
devices from bypassing the Name Server and talking directly to hosts.

Hard Zoning: - Hard Zoning uses the physical fabric port number of a switch to create zones and enforce the policy.

Pros:
- This system is easier to create and manage than a long list of element WWNs.
- Switch hardware enforces data transfers and ensures that no traffic goes between
unauthorized zone members.
- Hard zoning provides stronger enforcement of the policy (assuming physical security on the
switch is well established).

Cons:
- Moving devices to different switch ports requires policy modifications.

Broadcast Zoning: · Broadcast Zoning has many unique characteristics:
- This traffic allows only one broadcast zone per fabric.
- It isolates broadcast traffic.
- It is hardware-enforced.

If you ask me how to choose the zoning type then it is based on SAN requirement in your data center environment. But port zoning is more secure but you have to be sure that device is not going to change otherwise every time you change in storage allocation you have to modify your zoning.

Generally use in industry is soft zoning but as i have mentioned soft zoning has many cos. So, it is hard to say which one you should use always. So, analyze your datacenter environment and use proper zoning.

Broadcast zoning uses in large environment where are various fabric domain.

Having said that Zoning can be enforced either port number or WWN number but not both. When both port number and WWN specify a zone, it is a software-enforced zone. Hardware-enforced zoning is enforced at the Name Server level and in the ASIC. Each ASIC maintains a list of source port IDs that have permission to access any of the ports on that ASIC. Software-enforced zoning is exclusively enforced through selective information presented to end nodes through the fabric Simple Name Sever (SNS).

If you know about switch then you must notice that in Cisco we have FCNS database and Brocade Name Server. Both are for same purpose to store all the information about port and other. FCNS is stand for Fibre Channel Name Server.

There are plenty of thing on Switch itself to protect your SAN environment. Each vendor comes with different security policy. Zoning is the basic thing in order to secure your data access.

Hope this info will be useful for beginner. Please raise a comment if you want to know specific things.

If a LUN is allocated to a host thru 2 path, how many LUNs will be visible on the host.

Ans: 2 if no multipathing software is installed.