IBM Storwize V5020 User Manual (English)

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488 Implementing the IBM Storwize V5000 Gen2 with IBM Spectrum Virtualize V8.1

10.1.5 Application testing with FlashCopy

It is often important to test a new version of an application or operating system that is using

actual production data. This testing ensures the highest quality possible for your environment.

FlashCopy makes this type of testing easy to accomplish without putting the production data

at risk or requiring downtime to create a constant copy.

You create a FlashCopy of your source and use that for your testing. This copy is a duplicate

of your production data down to the block level so that even physical disk identifiers are

copied. Therefore, it is impossible for your applications to tell the difference.

10.1.6 Host and application considerations to ensure FlashCopy integrity

Because FlashCopy is at the block level, it is necessary to understand the interaction

between your application and the host operating system. From a logical standpoint, it is

easiest to think of these objects as “layers” that sit on top of one another. The application is

the topmost layer, and beneath it is the operating system layer.

Both of these layers have various levels and methods of caching data to provide better speed.

Because the FlashCopy sit below these layers, they are unaware of the cache at the

application or operating system layers.

To ensure the integrity of the copy that is made, it is necessary to flush the host operating

system and application cache for any outstanding reads or writes before the FlashCopy

operation is performed. Failing to flush the host operating system and application cache

produces what is referred to as a

crash consistent copy.

The resulting copy requires the same type of recovery procedure, such as log replay and file

system checks, that is required following a host crash. FlashCopies that are crash consistent

often can be used following file system and application recovery procedures.

Various operating systems and applications provide facilities to stop I/O operations and

ensure that all data is flushed from host cache. If these facilities are available, they can be

used to prepare for a FlashCopy operation. When this type of facility is unavailable, the host

cache must be flushed manually by quiescing the application and unmounting the file system

or drives.

10.1.7 FlashCopy attributes

The FlashCopy function in IBM Spectrum Virtualize features the following attributes:

򐂰 The target is the time-zero copy of the source, which is known as

FlashCopy mapping

targets

򐂰 FlashCopy produces an exact copy of the source volume, including any metadata that was

written by the host operating system, logical volume manager, and applications.

Preferred practice: From a practical standpoint, when you have an application that is

backed by a database and you want to make a FlashCopy of that application’s data, it is

sufficient in most cases to use the write-suspend method that is available in most modern

databases, because the database maintains strict control over I/O.

This method is as opposed to flushing data from both the application and the backing

database, which is always the suggested method because it is safer. However, this method

can be used when facilities do not exist or your environment includes time sensitivity.

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Quick Installation Guide204 pages

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IBM Storwize V5020 Specifications

General

Model	Storwize V5020
Category	Storage
Maximum Number of Drives	240
Form Factor	2U
Supported Protocols	iSCSI
Drive Types Supported	SSD, SAS, NL-SAS
Expansion Units	Up to 9
RAID Levels Supported	0, 1, 5, 6, 10
Host Interface	16 Gb FC, 10 Gb iSCSI
Interface Types	Fibre Channel, Ethernet, SAS
Power Supply	Dual redundant power supplies