write cache

Hotfix PVS710TargetDeviceWX64001 Is Out!

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Folks, I hope you had a great holiday season! The New Year for PVS has started with some exciting news about the new Write Cache option – Cache on device RAM with overflow on hard disk. Introduced with PVS 7.1, it is designed to provide faster performance than Cache on Device HD (which is the most popular method of caching these days) while at the same time fix an issue with Microsoft’s Address Space Layout Randomization (ASLR). The new cache uses a VHDX format which takes care of any issues you may have experienced with crashing applications and print drivers on your provisioned images due to a conflict with the ASLR technique which Microsoft developed to randomize areas of the code in memory and make it harder for hackers to predict the location of certain processes within an application.

With the initial release of PVS 7.1, however, there was an issue with turning on the RAM portion of this hybrid write cache, so you would’ve seen some performance improvement but not what you expected with RAM. The new hotfix PVS710TargetDeviceWX64001 fixes this issue and is now publicly available for download at CTX139850. 

It is a target-side patch so you will need to reverse image your vDisk to do the install. Good luck!

About That New Cache Type…

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As many of you have noticed, PVS 7.1 has a brand new cache type called “Cache in Device RAM with Overflow on Hard Disk.” This new feature of PVS is designed to provide better performance by combining the light speed of RAM with the efficiency of hard disk storage and at the same time avoiding previous hurdles such as unexpected BSOD when using RAM cache due to the memory getting filled up. The new differencing format of the file (VHDX) also resolves the issue when caching to device HD where applications accessing printer drivers would randomly crash.

As some of you have noticed, however, target device performance has not increased dramatically in terms of speed. In fact, some folks out there with IOMeters have reported that IOPs have not improved at all with the new cache type. This is currently a known issue due to a problem turning on the RAM portion of the cache and I know for a fact that Citrix is working on fixing it in the next hotfix release for PVS 7.1. So stay excited!

Edit:

The RAM portion of the this cache type is fixed in CTX140338 which is a target device hotfix.