AUTOMATION OF VPLEX REPLICATION USING REST API

Vijay GadwalSenior Application Developer II EMC Global Services

Terence JohnySolutions Architect EMC Global Services

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Table of Contents The need for REST API Integration ............................................................................................ 3

Architecture of the solution ......................................................................................................... 5

VPLEX Element Manager API .................................................................................................... 6

Overview ................................................................................................................................ 6

VPLEX Commands Used ....................................................................................................... 6

Replication Automation Script .................................................................................................... 8

Modules implemented ............................................................................................................ 8

Perl Script Design ................................................................................................................... 8

Bibliography ..............................................................................................................................10

Disclaimer: The views, processes, or methodologies published in this article are those of the

authors. They do not necessarily reflect EMC Corporation’s views, processes, or

methodologies.

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The need for REST API Integration

VPLEX® features such as non-disruptive data mobility across heterogeneous arrays, data

mobility across sites, and highly advanced cache coherency algorithms dissolve physical

barriers in and between data centers and open a whole new approach to data center design.

At the same time, customer investments in array-based storage replication play a very important

role in ITs new approach. While VPLEX as a product is designed to work with the existing array-

based replication tools—with VPLEX acting as the Virtualization layer—best practices and

special considerations need to be accounted for when the existing replication scripts need to be

leveraged.

This problem relates to a key requirement while using VPLEX with array-based storage

replication; the step to invalidate the read cache.

Since VPLEX leverages its data caching and distributed caching features, it becomes important

to invalidate the read cache for target volumes before new replication operations can be

performed on them. Performing replication operations on VPLEX virtual volumes directly can

potentially cause data corruption. This is due to the fact that replication operations are directly

performed on the backend array outside the VPLEX I/O path, causing the read cache of the

VPLEX to differ from the data on the physical disk on the array.

Expansion of this requirement comes into play when existing replication scripts need to be

leveraged and additional cache invalidation operations need to be run on the VPLEX virtual

volumes. Since the cache invalidation steps would need to be run separately on the VPLEX CLI,

the existing replication process would NOT continue to be a fully automated process, requiring

manual intervention for the VPLEX part.

The replications scripts also have to be modified to include the read cache invalidation steps

and require running on the VPLEX management servers at the specific points of the replications

scripts.

Now, consider developing these scripts and modifications on multiple machines and even at

multiple customer sites. This would involve investing in resource and time to understand each

environment, develop custom scripts for each site, and then run through a phase of test and

acceptance to ensure the proper operation of the complete replication cycle.

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This would then mean an additional investment from EMC into all sites where we deploy VPLEX

and follow the steps of discovery, design, and testing to make array-based replication in a

VPLEX based environment work.

We have devised a very simple and elegant solution that will leverage the REST API interfaces

already supported on VPLEX and that would not require modification to the existing customer

array-based replication automation scripts.

In this article, we describe the architecture of the solution and explain in detail the technical

components such as the operations supported using REST APIs, the steps necessary for the

array-based replication, various modules used, and the technologies used for the scripting.

Our solution has been successfully designed and implemented in a number of Fortune 500

companies and has saved several hours of work. The level of automation provided has an

immense impact on total customer experience (TCE) and requires low or no learning curve to

adopt this solution. The simplicity and innovative method we used can lead to wider use of this

solution to rapidly integrate array-based replication scripts for VPLEX environments.

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Architecture of the solution

The key operation for array-based replication in a VPLEX environment is the invalidation of the

VPLEX read cache.

This is achieved by executing these three steps.

1. Remove the Virtual Volumes (Replication Targets) from the VPLEX Storage View

- This will invalidate the read cache for the corresponding virtual volume.

2. Perform the Replication Operations

- Leverage existing array-based replication scripts.

3. Add Virtual Volumes to the VPLEX Storage View

- Maintains previous HLU information

These steps are fully automated with the help of VPLEX REST API Integration.

As part of the VPLEX 5.2 release, a new command has been supported to invalidate the read

cache directly instead of using the 3-step process outlined above for VPLEX 5.1.

Virtual-volume cache-invalidate

The solution has been implemented using a Perl script that leverages the VPLEX REST API

framework to execute remote commands on the VPLEX.

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VPLEX Element Manager API

Overview

VPLEX Element Manager API uses the Representational State Transfer (REST) software

architecture for distributed systems such as the World Wide Web. It allows software developers

and other users to use the API to create scripts to run VPLEX CLI commands.

The Element Manager API supports most VPLEX CLI commands apart from session aware

commands (i.e. pushd, popd), commands that manage files (i.e. getsysinfo), and commands

that manage the security aspects of the product.

VPLEX supports the following RESTful requests:

HTTPS GET - Performs an ls of a context and shows the context attributes and sub-

contexts

HTTPS PUT - Sets values for a writeable attribute

HTTPS POST - Executes a VPLEX CLI command

Command options are sent and responses are received as JSON strings.

URIs are used to identify VPLEX objects and contexts.

HTTP POST requests are used to execute the commands to modify the storage views in the

VPLEX (adding/removing virtual volumes).

VPLEX Commands Used

The following VPLEX CLI commands will be used in the solution, and will be executed over the

REST API requests.

ls -f --attribute/clusters/<cluster-name>/exports/storage-views/<storage-view-

name>::virtual-volumes

o Lists the virtual volumes that are part of a storage view

export storage-view removevirtualvolume –v <storage-view-name> -o <virtual-volume-

name> -f

o Removes the specified virtual volume from the storage view

export storage-view addvirtualvolume –v <storage-view-name> -o <virtual-volume-

name> -f

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o Adds the specified virtual volume from the storage view. The HLU number will

also be specified along with the virtual volume name.

virtual-volume cache-invalidate –v clusters/<cluster-name>/virtualvolumes/<virtual-

volume-name>

o Invalidates the cache of the specified virtual volume.

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Replication Automation Script

Modules implemented

VPlexRestApiScript.pl -- the main script which in turn calls the modules listed below based on

user parameters.

VplexListVirtualVolumes

VplexRemoveVirtualVolumes

VplexAddVirtualVolumes

VplexInvalidateVirtualVolumes (Only for VPLEX 5.2)

VplexListVirtualVolumes

This module will list all the virtual volumes that are part of a particular storage view in the

VPLEX, along with their HLU numbers. This can be used to generate a list of virtual volumes to

later filter them and retain only the virtual volumes that are participating in the replication

process.

VplexRemoveVirtualVolumes

This module will remove a list of virtual volumes from a particular storage view in the VPLEX. It

can either read a filtered list of virtual volumes from a file (generated by using the

VplexListVirtualVolumes module) or remove all the virtual volumes that are part of the storage

group.

VplexAddVirtualVolumes

This module will add a list of virtual volumes back into a particular storage view in the VPLEX. It

will read the list of virtual volumes to be added from a file that is generated while using the

VplexRemoveVirtualVolumes module. This module will retain the HLU numbers of the virtual

volumes while adding them back to the storage view.

VplexInvalidateVirtualVolumes

This module will invalidate the cache of all virtual volumes belonging to a particular storage view

in the VPLEX. It will read the list of virtual volumes to be invalidated using another command.

Perl Script Design

The perl script used to perform the automation uses the perl modules shown below to achieve

specific tasks.

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Net::HTTPS and Net::SSL

These modules are used to send HHTP request using SSL security to the VPLEX. The HTTP

requests are comprised of commands to be executed on the VPLEX.

JSON

This module is used to encode/decode data being passed/retrieved to/from the VPLEX. Data to

be sent for the VPLEX commands over the HTTP requests is sent in JSON format. This is a

standard format used along with REST API requests. The perl module encodes the data before

passing it to the VPEX and decodes from JSON format to normal perl format once the VPLEX

responds with the requested data.

Sending a HTTP request to the VPLEX

The code snippet shown below indicates the approach used to send the HTTP commands to

the VPLEX.

Reading the HTTP response from the VPLEX

The code snippet shown below indicates the approach used to decode and retrieve the data

from the REST API response obtained from the VPLEX.

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Bibliography

VPLEX – Powerlink documentation – http://powerlink.emc.com

VPLEX central – http://one.emc.com/clearspace/community/active/vplex_central

Perl – http://www.perl.org/

VPLEX Element Manager API – Element Manager API Guide P/N 302-000-281-01

REST API – http://en.wikipedia.org/wiki/Representational_state_transfer

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