If you had run HADR simulator before or read the HADR_sim page then you might have gone through the things I am explaining here. If not, then this might come in handy.
Recently, I was setting up a DB2 LUW HADR pair over a WAN and thought it might be a good idea to first run HADR Simulator to simulate HADR in the different sync modes and see which one best fits here. The binary for HADR simulator can be downloaded
here. The HADR_sim web page contains all the details on how to use the tool. When running the tool using one of the sync modes it is advised to provide details to -disk argument. The -disk argument takes in two values
1) data rate in MBytes/sec and
2) per write overhead in seconds.
The
HADR_sim page describes on how to calculate these two values. I will paste it here to ease reference:
"Disk speed
Simhadr can measure disk speed and simulate disk write.
To measure disk speed, use "-testDisk" option. To specify disk speed to simulation runs, use the "-disk" option.
Disk write time is modeled as: write_time = data_amount * write_rate + per_write_overhead. Write_rate is in unit of MB/second. Per_write_overhead is in unit of second. Theoretically, given the write time of two runs with different data amount, you can solve the equation and get write rate and per write overhead. To make things simple, you can do a run with 1 page flush size. The reported write time is an approximation of per write overhead. Then do a run with a large flush size such as 500 or 1000. The reported MB/second is an approximation of write rate.
When testing disk, simhadr issues synchronous write (write() does not return until data is on disk), just like log writing in real DB2. Simhadr does not remove the temp file created for disk testing. You may examine, then delete the file. For example, you may want to examing the content of the file, or the degree of sector fragmentation on the file.
With a single disk, typical write rate is 30 to 60 MB/second. Typical per write overhead is 1 to 20 millisecond. Newer disks usually have shorter per write overhead. Disk arrays may have better performance. A device with short per write overhead is recommended as log device.
Once you have the disk speed parameters, you may feed it back to simhadr using -disk option. When disk speed is specified, simhadr will compute the time needed to write a log flush and use sleep() to simulate the write. No actual data is written. This allows you to use hypothetical disk speed for "what if" questions like "what if my disk is faster?".
