IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

Chapter 14. Copy Services for the DS6000 441

Figure 14-2 FlashCopy interfaces and functions

14.2.2 Performance considerations with FlashCopy

The FlashCopy guidelines and recommendations that we discuss in this chapter are fairly

generic. At the time of this writing (August 2005), FlashCopy services on the DS6000 have

not been benchmarked. Therefore, no specific guidance can be given for the throughput

characteristics of FlashCopy.

There are a number of considerations on FlashCopy performance, which we discuss in this

section:

򐂰 Time necessary for FlashCopy to complete

򐂰 Application downtime

򐂰 Background copy

򐂰 FlashCopy priority

򐂰 Physical relationship between source and target volume

Time required for FlashCopy to establish the copy relationship

FlashCopy operates on an entire logical volume. The process of establishing the copy

relationship and making the copy available for a few volumes takes typically a few seconds.

The establish times for two hundred volumes should be under 30 seconds. The size of the

logical volume makes very little difference to this time. When requesting the background copy,

the establish times can be slightly higher.

Application downtime during backups

With traditional backup methods, applications had to be stopped for the duration of the

backup, which could take a long time. With FlashCopy, the application only needs to be

stopped (quiesced, put into backup mode, etc.) for a minimal amount of time, just the very

short duration of the FlashCopy initialization (establish) time. Then the optional background

physical copy proceeds in parallel with the application doing its normal read and write activity,

unaware of FlashCopy activity. The FlashCopy target would be used as the backup source of

data for the backup application. The backup activity would continue independently of the

original FlashCopy source, which could have been put back into normal production mode by

the application as soon as the FlashCopy initialization was complete.

Persistent Flashcopy

Reverse restore,

fast reverse restore

Remote FlashCopy

Incremental FlashCopy

Target on existing Metro Mirror or

Global Copy primary

Consistency Group FlashCopy

Multiple relationship FlashCopy

DS CLIDS SM

DS front endsInterface

Function