Random application fails when using Standard Image mode with the Write Cache on Target Hard Disk option.

To resolve the issue, Citrix has provided a new write cache mode from Provisioning Services (PVS) 7.1. The server and the target must be on PVS 7.1 or higher and the cache type Cache in Device RAM with Hard Disk Overflow must be selected.

Problem Cause

With the release of Windows Vista, Microsoft introduced a security feature called Address Space Layout Randomization (ASLR). This feature randomized the memory address space of known Microsoft modules. When using the Write Cache on Target Hard Disk in PVS, applications and services have been found to randomly fail. There have been some known incompatibilities with the Microsoft Windows ASLR when using the Write Cache on Target Hard Disk option. This behavior can occur when data is written to the write cache and recalled into memory because of the method used by PVS to write the data to the write cache.

When using cache on device hard disk, PVS modifies the Memory Descriptor List (MDL) and then PVS writes the data to the local write cache. After the data is read by the Operating System, the ASLR triggers an exception due to the updated MDL.

• PVS 6.1 HF 20 - Possible issue with Address Space Layout Randomization (ASLR)

• Turbo Charging your IOPS with the new PVS Cache in RAM with Disk Overflow Feature!

For more information on ASLR, refer to the following links:

• Microsoft Security Intelligence Report

• Address space layout randomization