DataKeeper for Windows All Documentation - SIOS

Increase the WriteQueueLowWater TunablebytesDivide the result by 64K (65,536 bytes) to get the number ofblocks/bits821,412,495,360 / 65,536 = 12,533,760blocks/bitsDivide the resulting number of blocks/bits by 8 to get the bitmap filesize in bytes12,533,760 / 8 = 1,566,720So a mirror of a 765 GB volume would require 1,566,720 bytes forits bitmap file, or approximately 1.5 MB.A simple rule of thumb to use is that each GB of disk space requires 2 KB of bitmap file space.Remember to reserve room for all mirror targets (if you have multiple target systems, each oneneeds a bitmap file). Also remember to reserve room for all mirrored volumes.Increase the WriteQueueLowWater TunableIn order to increase throughput during a mirror Resynchronization operation, you may need toincrease the WriteQueueLowWater value for the mirror. If your mirror is currently in theMirroring state, you can safely change this value without pausing the mirror.If your mirror is currently resyncing, you can pause the mirror and change theWriteQueueLowWater value to any value less than the mirror's WriteQueueHighWatervalue. The default WriteQueueLowWater value is 150. Raising it to 2000 commonlyimproves resynchronization speed. Each environment is different, so you may find that a certainWriteQueueLowWater setting gives you the best resynchronization throughput. To changethe value, follow these steps:1. Start on the mirror source server. If resyncing, pause the mirror.2. Via your registry, go to the following:HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\ExtMirr\Parameters\Volumes\{GUID-for-VOLUME}\Targets\3. Right-click on the WriteQueueLowWater entry and Select Modify.4. Change the Base value to Decimal.5. Change Value data from 150 to 2000.• Update these registry changes in order to pick up and use these new values via the READREGISTRYcommand.• Make the above changes on all other targets/systems in the cluster.DataKeeper for Windows Technical DocumentationPage 37