Last updated: June 19th @ 176K downloads (added tape issues reported after U4b installation)
#0: vSphere Essentials 5.0 and 5.1
Symptoms: This limitation is documented in the release notes, but I'm still putting it here for better visibility: processing of VMs on ESXi 5.0 and 5.1 hosts licensed with VMware Essentials fails with the "The host is not licensed for this feature" error due to the bug in VDDK 5.5.5
Cause: Bug in VMware VDDK 5.5.5, while earlier VDDK version couldn't be shipped as a part of U4 due to security vulnerabilities.
Status: The following hot fix brings back an earlier VDDK 5.5 version as a workaround > KB2875 (hot fix package for U4a is available through support).
#1: Hyper-V
Symptoms: On Hyper-V versions prior to 2016, backup and replication jobs without application-aware processing enabled failing with "The system cannot find the file specified" error.
Cause: The issue is caused by snapshot path in VM configuration being different from the actual path on a file system in terms of symbols capitalization. We're not sure yet how such configuration appears in the first place, but it looks to be common for the impacted Hyper-V versions.
Status: Fixed in U4a. To resolve the issue in U4, either change the snapshot path in VM configuration, or install the hotfix > KB2890
#2: Backup console
Symptoms: Backup console failing to open after upgrade with "Object reference not set to an instance to an object" from backup console or "Could not load file or assembly" error in the logs (these are similar but separate issues, so they are tracked separately)
Cause: This looks to be caused by some uncommon Group Policy settings that prevents validating signature on some of the loaded libraries. This issue is still being investigated, however all support cases so far seem to be coming from high security environments with non-default settings (like U.S. federal customers), so we believe this issue should not affect most customers.
Status: Fixed in U4a. Hotfix for U4 is available through support.
#3: SureBackup on vSphere
Symptoms: SureBackup jobs failing due to lack of disk space in the vPower NFS cache folder.
Cause: Virtual Labs get their Redirect writes option reset during the upgrade, so writes are no longer redirected to the previously selected datastore.
Status: Fixed in U4a. For, U4 you can just set this setting manually, or use a hot fix that will restore pre-upgrade settings automatically for environments with large number of virtual labs > KB2885
#4: Unwanted email notifications
Symptoms: After upgrade, you may starting receiving failed protection group rescan reports.
Cause: Bug due to the introduction of an option to automatically assign a license to all incoming standalone agents.
Status: Workaround: go to the Inventory node, then under Protection Groups right-click the Manually Added group, and select Disable.
#5: Application-aware processing for Windows XP guests
Symptoms: Backup of Windows XP SP1 VMs fails with the "Failed to call RPC function Vss.GetFileFromGADir" error.
Cause: Windows XP has been EOL for almost 4 years now
Status: Fixed in U4a. For U4, the workaround is to disable application-aware processing for Windows XP guests.
#6: Upgrade
Symptoms: Upgrade to Update 4 fails with the "Database version downgrade detected ... Reboot and restart the setup" error.
Cause: Day/time value parsing bug on machines using certain Regional format OS settings where system time format uses a.m. and p.m. (lowercase with dots), for example: New Zealand, Romania, and most LATAM countries.
Status: Fixed in U4a. For U4, the workaround is described here KB2884
#7: Upgrade
Symptoms: Upgrade to Update 4 fails with the "Failed to install file system drivers" error.
Cause: Windows OS on the backup server is missing Windows Updates.
Status: Install the latest security updates, particularly Windows6.1-KB3033929-x64 > KB3033929
#8: Backup to tape job with backup copy job as a source
Symptoms: Tape job does not copy source backup files and finishes with No backup files found or No new files found message.
Cause: Backup copy job is set as source job for backup to tape.
Status: Hot fix for U4a and U4b is available here > KB2975
#9: Tape hardware encryption
Symptoms: Reduced backup to tape performance and [MT]SCSI PASS THROUGH DIRECT ended with Scsi Error Fixed format, current; Sense key: Illegal Request. or Error --tr:Failed to enable hardware encryption while restoring from tape after installing Update 4b.
Cause: Software encryption is incorrectly used instead of hardware encryption when the tape library's hardware encryption setting is set to "Application managed".
Status: Hot fix for U4b is available > KB2981