IBM System Storage DS6000 Series: Copy Services in Open Environments

302 IBM System Storage DS6000 Series: Copy Services in Open Environments

Example 23-2 shows the lspprc command that reports the Out Of Sync Tracks by volume

level. Here, we see that two volumes in LSS 14 have no Out Of Sync Tracks and two volumes

in LSS 15 have some number of Out Of Sync Tracks.

This particular configuration has source and target FlashCopy volumes within the very same

rank. Either you can consider putting one of the two busy volumes in LSS 15 into LSS 14 in

order to distribute the load over both LSSs, or another approach is to configure the

FlashCopy source volume and its corresponding target into different ranks or LSSs. See 23.4,

“Remote storage disk subsystem configuration” on page 299.

Example 23-2 Out Of Sync Tracks shown by the lspprc command

dscli> lspprc -l 1400-1401 1500-1501

Date/Time: November 21, 2005 10:58:39 PM JST IBM DSCLI Version: 5.1.0.204 DS: IBM.1750-1300819

ID State Reason Type Out Of Sync Tracks Tgt Read Src Cascade Tgt Cascade Date Suspended SourceLSS

=====================================================================================================================

1400:1A00 Copy Pending - Global Copy 0 Disabled Disabled invalid - 14

1401:1A01 Copy Pending - Global Copy 0 Disabled Disabled invalid - 14

1500:1B00 Copy Pending - Global Copy 31982 Disabled Disabled invalid - 15

1501:1B01 Copy Pending - Global Copy 51856 Disabled Disabled invalid - 15

When the load distribution is unknown in your configuration, you might consider developing

some rudimentary code based on for example, a script, which regularly issues the

showgmiroos commands as shown in Example 23-1 on page 301 and the lspprc -l

command as shown in Example 23-2. You can then process the output of these commands to

better understand the write load distribution over the Global Copy source volumes.

Note that the numbers in Example 23-1 on page 301 might be just a brief peak period. It is

still feasible to use the conventional approach with I/O performance reports, such as iostat in

the UNIX environment, to investigate the write workload. Or, you can use Tivoli Productivity

Center for Disk to analyze the storage disk subsystem performance.

23.6 Growth within Global Mirror configurations

When you add a rather large number of volumes at once to an existing Global Mirror session,

the available resources for Global Copy within the affected ranks might be overutilized or

even monopolized by the initial copy pass. To avoid too much impact, consider adding many

new volumes in stages to an existing Global Mirror session. If possible and as a rough

general rule, add only a few volumes in a rank during application peak I/O periods. Once the

first initial copy is complete, add the next few volumes. Again, as a general rule, plan for

adding one or two volumes in a rank during peak I/O load for the first initial copy pass. If

possible, then plan a massive add of new Global Copy volumes into an existing session

during off-peak periods.