Lead Time™ FAQ

1. What is the workaround for “zero service time” error in Remote Copy models

A problem in the current release of Lead Time (3.700) may cause a failure in certain models of Remote Copy configurations resulting in the run time Lead Time error message “zero service time”. This failure is due to the value of compression ratio on the Remote Copy link being incorrectly set to 0. A workaround is to manually set this value to 1 (or the appropriate non-zero value) in the dialog of link properties. This error should only affect models for which the compression ratio appears in the remote link properties dialog.

2. How do I minimize model Priming problems?

Model Priming is an automatic model calibration function built into Lead Time. Before you attempt to Prime a model, make sure that your model matches the configuration for which the data you are using for Priming was collected. A few particular points. Certain Priming options are set in Execution and miscellaneous panel (Options in Set menu). These options persist from one Lead Time session to another. Thus, if you check the skip buffer hits option for STK controllers, and later want to prime a model of, say, EMC Symmetrix, be sure to uncheck the “skip buffer hits” option before Priming. To avoid undesirable secondary effects when Priming models with RAMAC Array Subsystem and RAMAC with 3990 Mod 6 controllers, we suggest that you avoid using the “all of the above option” in Prime dialog. Instead, perform model initialization in two steps. First, initialize block lengths, then I/O variability using the appropriate options in the Prime dialog.

3. How do I get Lead Time to use more than 8 channels in a configuration? 

If you specified a configuration with more than 8 channels, and Lead Time uses only 8 of them, the most likely cause is that there is only one Channel Path Group defined and/or used. A single Channel Path Group in Lead Time is limited to 8 channels, so that you need to appropriately increase the number of Channel Path Groups. The number of Channel Path Groups is specified in the Configuration panel (Defaults in Build menu). In most cases, Lead Time will attempt to “evenly” utilize the Channel Path Groups defined but you may want to check and modify this default assignment in the Volume panel (Defaults in Build menu).

4. How do I represent mixed RAID array size configurations with the STK 9393-6?

To specify an array configuration with the STK 9393-6 control unit, all you need to do is to correctly set the number of physical drives. Note that this number must not include spares, i.e., Lead Time considers that the array sizes are 15 (13+2) and 7 (5+2). Based on the number of physical drives you specify in the Configuration panel (Defaults in Build menu), Lead Time automatically determines the corresponding RAID array configuration. You can view the resulting configuration using Banks of devices in the Configuration panel.

5. How do I represent mixed configurations with the HDS 7700-E?

To allow the representation of dual drive configurations with the HDS 7700-E controller, use the Control Unit panel (Defaults in Build menu). Uncheck the “single drive type” check box, and then select the correct drive types from the menu or specify yourself the appropriate drive parameters. Use the Device Controllers (Default, Configuration in Build menu) to specify the drive type for each ACP pair, as well as the applicable mapping parameters (number of physical drives per group, number of logical volumes per group). Lead Time mapping functions have been enhanced to account for multiple group characteristics. You can also individually specify the drive type for each RAID bank (array) or linear map. This allows to represent different drive types on a single ACP pair.

6. How do I model Remote Copy configurations?

In Lead Time, each controller is represented by a separate model (.MDL file). The Remote Copy relationship is defined through a new notion in Lead Time: that of a model folder. Access to folder related functions is through the Remote Copy options in the Model menu. The folder is used to specify which control units (i.e. models) are involved, the type of physical connection used (e.g. dedicated fiber, or common carrier), the number of logical links between the controllers over the physical connection(s), as well as the logical volumes subject to remote copy. The type of remote copy (synchronous or not) can also be specified for individual volumes. Lead Time automatically updates the model of the secondary control unit to account for the remote copy volumes as you specify them in the model of the corresponding primary control unit. This means that Lead Time modifies the model files specified in the folder as you update your Remote Copy definition. We strongly suggest that you create a backup copy of the model files before you include them in a folder, at least until you feel comfortable with the automatic modifications Lead Time performs. Since the model files must exist in order to be included in a folder, the Create option is provided to allow you to create an “empty” shell model for a secondary control unit.

7. How do I represent asymmetric configurations with the HDS 7700?

The representation of asymmetric configurations with the CPX Tetragon 2000 / HDS 7700 controller has been greatly simplified. Use the Device Controllers (Default, Configuration in Build menu) to specify the number of RAID banks on each DAP/ACP pair. More information in the Lead Time help file. The same approach can be used to model RAMAC configurations with 8 Device Controllers.

8. I am mostly interested in numbers, and I find that the graphs slow me down. How do I disable them?

It is now possible to disable the results graphs and/or the configuration display. Use the Other option in the Set menu. We have also added the option to skip the initialization of block lengths when Priming models. This is useful in situations where the exact number of bytes transferred per I/O is known. Additionally, it is possible to skip the initialization of I/O variability. This can significantly speed up the Prime and especially the Join Prime functions. There is some loss of accuracy. Its extent can be assessed using the Absolute option in the View menu after the model has been primed.

9. How do I examine and modify the mapping logical to physical for Array Controllers?

To assist in configuring models with array controllers, a Logical device mapping display has been added. This display shows and lets you modfiy the mapping between logical devices and physical DASDs or RAID groups. The See button in this dialog, lets you toggle between the display in current device group order and a display ordering by physical devices or RAID groups. In addition to the standard order based mapping used in previous versions of Lead Time, we have included an option which attempts to distribute the logical devices so as to balance the workload at the back end of the controller. To use this option, select the appropriate button before pressing the Remap pushbutton. Both the Remap function and the Logical device mapping display are accessible through the Default mapping button in the Build Defaults dialog.

Also, it is now possible to specify default mapping for Disk Array controllers in terms of how many logical volumes should be mapped by default onto a specifed number of physical DASDs. This parameter is accessible through the Default maps push-button in the Defaults dialog (Build menu). See also Lead Time help article on Modelling Array Controllers. The same dfialog allows to change the size of the RAID group although this not encouraged.

10. What about printing or saving the comparison report?

The Comparison report between a base model and the current one has been added to the series of reports that can be printed or saved in a file. You can disable it using the Report option in the Set menu.

11. How do I quickly move the volumes with non trivial activity from one controller to another?

To simplify reconfiguration studies, the Express facility has been added to the Merge option (File menu). In a single step, it allows you to merge the device groups of your guest model. For more information, please review the Merge item in the Lead Time Help file. You can specify a threshold so as skip low activity volumes from the merge. You can also remove low activity device groups using the new Prune option in the Build Move menu.

12. I have noticed a change in some parameters for the HDS 7690 controller. How does it affect existing models?

The interpretation of parameters for Intelligent Loading with the CPX 6090-6 / HDS 7690 has been changed to bring it in line with that for IBM 3990 Model 6 and CPX Tetragon 2000 / HDS 7700. For all controllers, the adaptive staging is now represented through percentages of Full track, Partial Track (and Record Only) staging. GTFSIM has been modifed accordingly. Lead Time automatically compensates for the difference in interpretation when retrieving models created under older versions.