LUN and RAID Group CREATION

7/21/2019 LUN and RAID Group CREATION

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2003 EMC Corporation. All rights reserved. 11

LUN and RAID Group Expansion


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LUN Expansion with MetaLUNs

MetaLUN 11

HOST

LUN 11

R5, 4+1

LUN 12

R5, 4+1

LUN 13

R1/0, 4

LUN 14

R1

LUN 15

R5, 8+1

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. The attached host sees

one large LUN and is unaware of the component LUNs as they are made private

when combined into a metaLUN. Like a LUN, a metaLUN can belong to a

Storage Group, and can participate in SnapView, MirrorView and SAN copy

sessions. MetaLUNs are supported only on CX-Series storage systems.


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Expansion by Concatenation

Base LUN Comp B

New

Capacity A

Comp A

New

Capacity B

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 re-striping of data between the original storage and the

new LUNs. The components may be different RAID types and different

capacities. The chief advantage of the concatenate operation is that it completes

immediately. While this is not the recommended long-term solution it does

provide for a fast, flexible expansion but may have a negative impact on

performance if LUNs of different RAID types are used.


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Expansion by Striping

FLU x

Unused

Capacity

metaLUN 0

Before:

Unused Capacity

After:

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.

Components LUNs must be of the same RAID type and they should be the same

size. Excess blocks in each LUN (based on smallest LUN) are wasted space,

because they will be ignored by FLARE. The striped metaLUN has the advantage

of higher spindle counts for improved performance. The stripe expansion may

take a long time to complete. The process concatenates new storage space, then

re-stripes existing data across all spindles in the new space. The original space is

available during the entire operation and the additional space can be made

available after re-striping is complete. Striped expansion can take a significant

period of time to complete.


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MetaLUN Limits

CX600

CX400

CX200

Max number of

components

per metaLUN

Max number of

FLARE LUNs per

striped component

16

8

8

32

32

16

In a CX600 array, a metaLUN can consist of a maximum of 16 components and a

component can consist of a maximum of 32 striped FLARE LUNs.

In a CX400 array, a metaLUN can consist of a maximum of 8 components and a

component can consist of a maximum of 32 striped FLARE LUNs.In a CX200 array, a metaLUN can consist of a maximum of 8 components and a

component can consist of a maximum of 16 striped FLARE LUNs.


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LUN Expansion Rules

Striped expansion: FLARE LUNs within a striped

component must be the same RAID type

the same size (in blocks)

the same disk type (Fibre Channel vs. ATA)

Concatenated expansion: All components withinmetaLUN must be either all protected (1, 1/0, 3, 5) or all non-protected (0)

the same disk type (Fibre Channel vs. ATA)

Expansion LUNs must not be consumed by another driver

private or transitioning

Striped expansion and concatenated expansion each have a unique set of rules.

When expanding a LUN into a striped metaLUN, all the LUNs participating in the

metaLUN component must be protected by exactly the same RAID scheme, be

exactly the same size, and must all be of the same disk type either Fibre Channel

or ATA.

When expanding a LUN into a concatenated metaLUN, the rules are less

restrictive. The LUNs participating in the meatLUN component must all be either

protected or unprotected, can be any size, and must be either all Fibre Channel

or all ATA.

The expansion LUNs must not be part of a snapshot, clone, mirror or SAN Copy

session and must not be part of a Storage Group. Also they are not allowed to be

private LUNs or in a transitioning state.


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Concatenate Expansion Walk-Through

To expand a LUN, right click the LUN to be used as the Base LUN and select

Expand from the menu. Remember that the LUN ID information of the Base

LUN will be inherited by the metaLUN.

LUN expansion is initiated through the use of a wizard. The wizard introduction

screen states the objective of the wizard and clicking Next will start the definition

process. At any point in the process clicking Cancel will abort.


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Select Expansion Type

Before any choices can be made for the component expansion FLARE LUNs, the

expansion type must be selected. Both options, Stripe Expansion or Concatenate

Expansion are briefly described and either type may be selected. This walk-

through will show a concatenated expansion.


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Select Unused LUNs

The wizard will present all unconsumed (unused) LUNs in the array without

regard to Storage Processor ownership. The only restriction to the presented list

is that the LUNs to be used for expansion must be protected (RAID 1, 1/0, 3, or

5) if the Base LUN is protected. Notice that LUNs of all sizes are listed.


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Expansion LUN Selected

Once expansion LUN(s) are selected the wizard will automatically calculate the

maximum user capacity. Click Next to proceed with the wizard.


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Specify MetaLUN Capacity

A very important consideration when expanding LUNs is the affect on the host file

systems. If the target host system OS can not handle dynamic changes to the

volume size, host contact with the data in the Base LUN may be interrupted.

The option of leaving the metaLUN presented to the host at the original BaseLUN size may be selected by clicking Current Capacity. Presenting the

Maximum Capacity or a user defined Other Capacity are also available. If

Other Capacity is selected, the value entered must be a whole number as

decimal values are not allowed. For example, if 1.5 GB is to be made available

the value must be entered as 1500 MB. For this walk-through, Maximum

Capacity has been selected. Click Next to proceed with wizard.


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Specify MetaLUN Settings

MetaLUN Name by default is inherited from the Base LUN.

The Default Owner Storage Processoris the SP that assumes ownership of the metaLUN when thestorage system is powered up and is inherited from the Base LUN and can be user set.

The Expansion Rate will set the relative priority of expansion activity in relation to host I/O. It may be set tolow, medium, high, or ASAP. The higher the expansion rate the more impact on system performance.Because a concatenated expansion does not need to re-stripe data the expansion rate has no impact on theconcatenated expansion or host I/O performance.

Stripe Element Size: If multiple LUNs are contained within a component within the metaLUN a new stripeelement size will be calculated. The size is based on the first LUN in the component and is calculated bydetermining the stripe size of the first LUN (# of data disks x LUNs stripe element size) and multiplying thatby the Element Size Multiplier. For example, to determine the stripe size of a 4 + 1 RAID 5 LUN with a stripeelement size of 128 sectors, you multiply 128 by 4 for a stripe size of 512 sectors or 256KB of data.Multiplying 256KB by an Element Size Multiplier of 40 (the default) will create a metaLUN element size of10MB. FLARE would write 10MB of data to a LUN in the striped metaLUN component before proceeding tonext LUN in that component. The stripe element size for each component in the metaLUN can be differentsince the stripe size of the first LUN in each component can vary. Valid element size multiplier values are 1through 255.

Alignment Offset specifies the offset for a LUNs RAID stripe alignment when the host operating systemrecords private information at the start of the LUN. The default value is zero and this supports most hostoperating systems. Alignment Offset is available only when the LUN you are expanding meets one of thefollowing conditions: The LUN is in or out of a Storage Group and has no existing data, or the LUN is not in aStorage Group, has existing data, but you do not want to preserve this data.

Problems can arise when a host operating system records private information at the start of a LUN. This caninterfere with the RAID stripe alignment so that when data I/O crosses the RAID stripe boundary, thestorage-system performance is degraded. In order to properly use Alignment Offset, you must know theexact size of the private information. Improper use will degrade performance.


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Expand LUN Summary and Confirmation

The final step in the wizard is to provide the user with a summary of the actions

about to performed. If any of the expand parameters need to be changed theBack button can be used to access the appropriate wizard page. If all parameters

are acceptable, click Finish to initiate the expand action. The system will notify

the user that the expand has been initiated.


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Navisphere Manager View

At the conclusion of the expand activity, the new metaLUN is displayed in

Navisphere Manager with its component parts viewable. Note the icon change

and the renumbering of the component FLARE LUNs while the metaLUN

inherited the Base LUNs ID.


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Stripe Expansion Walk-Through

Performing a striped expansion is initiated in the same manner as a concatenated

expansion, right click the LUN to be used as the Base LUN and select Expand

from the menu.


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Expansion LUN Selection

This screen in the wizard represents the branching point between concatenated

expansion and striped expansion. For this walk-through Stripe Expansion is

selected. After the expansion type is selected, clicking Next will proceed. As with

concatenated expansion, this process can be aborted or backed-up at any point

until the final action is committed.

A major difference between concatenated expansion and striped expansion is the

LUNs presented for inclusion. Concatenated expansion was allowed to include all

free LUNs of any size while striped expansion may include only LUNs which are

exactly the same size as the Base LUN. For this walk-through two expansion

LUNs have been selected for inclusion.


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metaLUN Settings

As with the concatenated expansion, striped expansion allows the entire

metaLUN to become host visible, or size may be restricted to the current Base

LUN capacity and enlarged later, or a value between current and maximum may

be user selected. Remember, whole numbers only in this last option.

Here the metaLUN name has been changed from the default and the expansion

rate set at ASAP. The element size multiplier is left at the default value of 40 and

if the Base LUN has a default stripe size will result in 10MB of data being written

to a LUN within the metaLUN before proceeding to the next LUN in the metaLUN.

This will greatly reduce the amount of addressing calculations and disk seeks on

the backend and will result in greater performance than if the element size of the

metaLUN matched the Base LUN exactly.


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Expansion Wizard Final Step

The wizard provides a summary of the action to be performed and allows a final

chance to abort the action or change any and/or all the parameters. Once Finish

has been selected, the action will initiate and the system will provide confirmation.


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Striped MetaLUN Components

After the expansion is completed, the metaLUN will be visible in Navisphere

Manager. Here it can be seen that the metaLUN inherited the LUN ID of the Base

LUN which in turn was renumbered along with the expansion LUNs and that all

three LUNs comprising the metaLUN are considered to be a single component.


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MetaLUN Properties

MetaLUNs like FLARE LUNs have a Properties sheet. Right-click the metaLUN

and select Properties to open this dialog box. While the metaLUN is expanding

its progress may be tracked on the General tab. The Expansion Rate for an

expanding metaLUN may not be changed but can be changed after the current

expansion is complete. The User Capacity can also be altered on this page but

caution should be exercised when performing this action as some operating

systems may not contain functionality to perform dynamic expansion.


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Expanding RAID Groups

DriveDrive

11DriveDrive

00DriveDrive

22DriveDrive

33DriveDrive

44DriveDrive

66DriveDrive

55DriveDrive

77DriveDrive

88DriveDrive

99

RAID 5 GroupRAID 5 Group

Available DisksAvailable Disks

DriveDrive

11

DriveDrive

00

DriveDrive

22

DriveDrive

33

DriveDrive

44

RAID 5 GroupRAID 5 Group

DriveDrive

55

DriveDrive

66

DriveDrive

77

DriveDrive

88

DriveDrive

99

Available DisksAvailable Disks

RAID Groups can be expanded even after creation and even when they

have active LUNs bound to them.

If a RAID Group has not reached its drive limit (highlighted earlier), it can be

expanded by addingAvailable drives. In other words, drives not belonging

to any RAID Group.

The above RAID 5 Group begins with 5 disks, which is below the RAID 5limit of 16. Drives 5 and 6 are not currently in a RAID Group so they can be

added to this group. The end result is a 7-disk RAID 5 Group.


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Expanding RAID Groups Multiple LUNs

00 11 22 33 44

00 11 22 33 44 55 66

LUN 0LUN 020 GB20 GBLUN 1LUN 120 GB20 GB

LUN 2LUN 220 GB20 GB





LUN 3LUN 3

20 GB20 GB

Free SpaceFree Space

Before Expansion

After Expansion

If there are multiple LUNs bound to a RAID Group, the LUNS will not change

size during expansion. They will be re-striped across all of the disks in the

expanded group and retain their original characteristics. The expansion

process creates a large pool of free space at the bottom of the RAID

Group for adding of additional LUN(s).


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Expanding RAID Groups Single LUN

00 11 22 33 44

00 11 22 33 44 55 66



Before Expansion

After Expansion

In this example, a single LUN is bound to the RAID Group, and it is bound to

the maximum capacity. When the RAID Group is expanded, and the option

to Expand LUN with Raid Group is checked, that LUN will be expanded.

Though the physical disk size will be increased for the host, some hosts will

not automatically stretch the partitions on the drive.

If the option to Expand LUN with Raid Group is not checked, the LUN willremain the same size.


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Expanding RAID Groups

To expand a RAID Group, right-click on the RAID Group you wish to expand and select

Properties. Once in the RAID Group Properties box, select the Disks tab. That will show

all disks currently in the RAID Group. Click on the expand button to select from the

remaining unbound disks on that array. You will also see the option to Expand LUN with

Raid Group.


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Defragmenting RAID Groups

00 11 22 33 44 55 66LUN 0LUN 020 GB20 GB

Free SpaceFree Space20 GB20 GBLUN 2LUN 220 GB20 GB


Free SpaceFree Space60GB60GB Largest LUN = 60GB

00 11 22 33 44 55 66LUN 0LUN 020 GB20 GB



Free SpaceFree Space80GB80GB Largest LUN = 80GB

After Defragmenting

A LUN can only be created using contiguous free space. In the top

example, a user has removed a LUN created earlier. This created a 20 GB

gap in the LUN stack. There also is 60 GB free space at the bottom of the

stack. The user can create a 20 GB LUN and a 60GB LUN, but he can not

create an 80 GB LUN.

If the user defragments the RAID Group, it will consolidate all Free Space inthe RAID Group, allowing for the creation of a single, larger LUN.


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Defragmenting RAID Groups

LUN 0 (5.000 GB). Offset 0.000 GB, Owned by - DATA-01LUN 1 (5.000 GB). Offset 5.000 GB, Owned by - DATA-01LUN 3 (5.000 GB). Offset 15.000 GB, Owned by - DATA-01

LUN 6 (5.000 GB). Offset 30.000 GB, Owned by - DATA-01LUN 7 (5.000 GB). Offset 35.000 GB, Owned by - DATA-01LUN 8 (5.000 GB). Offset 40.000 GB, Owned by - DATA-01

To Defrag a RAID Group, right-click on the RAID Group you wish to expand

and select Properties. Once in the RAID Group Properties box, select the

Partitions tab.

The Partitions tab lets you view the current partitioning of a RAID Group

and lets you defragment (consolidate the data on) the disks in a RAID

Group.LUNs List of LUNs currently bound in this RAID Group.

RAID Group Partitions Graphical representation of arrangement of LUNs

and distribution of free space associated with this RAID Group.

Defragment Begins the RAID Group defragmentation process.


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Summary

metaLUNs Striped Concatenated

Expand / Defrag RAID Groups Multiple LUNs

Single LUNs

Documents

LUN and RAID Group CREATION