I recently had a perplexing problem on one of my lab servers, which took a lot of head-scratching to solve. Fortunately I had some time to burn so I managed to get to the bottom of it.
Symptom
If I moved a disk or a CSV to a specific node in my Hyper-V failover cluster it would put the CSV in redirected mode and log the following to the System log
Log Name: System
Source: Microsoft-Windows-FailoverClustering
Event ID: 5125
Task Category: Cluster Shared Volume
Level: Warning
Keywords:
User: SYSTEM
Description:
Cluster Shared Volume '\\?\Volume{0bf0b229-9b0e-11e1-8a3a-e4115ba98410}\' ('') has identified one or more active filter drivers on this device stack that could interfere with CSV operations. I/O access will be redirected to the storage device over the network through another Cluster node. This may result in degraded performance. Please contact the filter driver vendor to verify interoperability with Cluster Shared Volumes.
Active filter drivers found:
aksdf (Encryption)
Cause
After a fair bit of head-scratching, rolling back actions and research with Sysinternals Process Monitor I pinpointed the problem to NetApp Single Mailbox Restore for Exchange. During installation it installs the aksdf.sys device driver. A quick google search showed it to be a driver used for USB dongle licensing. Weird, since SMBR does not require a dongle. Anyhow, this device driver conflicts with the CSV and forces it to run in redirected mode
Solution
The solution is simple – navigate to the HKLM\SYSTEM\CurrentControlSet\Services\akdsf registry key and set the Start key to have a value of four (4), as per the below screenshot.
This is not documented anywhere on the NetApp support site, so I will file a bug report. In mitigation, I cannot see that one will actually run SMBR on one of your production cluster nodes. Still, it should be trivial for NetApp to patch their installation routine to not install the aksdf.sys device driver.
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