Recently my colleague Martijn Moret, backup & datamanagement consultant at PQR, informed me on possible backup/restore issues when using vSphere VDDK 5.1. The VDDK is Virtual Disk Development Kit and used by 3rd party backup software in conjunction with vSphere.
VMware documented this issue in KB article 203993: “This article describes an issue with the VMware Virtual Disk Development Kit (VDDK) that may cause backup and restore operations to hang or fail. Third-party backup vendors that are using the VMware VDDK may encounter backup or restore issues when backing up VMware vSphere environments.“Symantec also published an article on the issue, in which Symantec/VMware suggests that “any 3rd party vendor depending on the current API cannot perform consistent backups and cannot ensure a reliable recovery point.”
This doesn’t say that every backup vendor is using VDDK 5.1 in a vSphere 5.1 environment, it seems VDDK 5.0 (which doesn’t has this issue) is also used by some backup vendors in vSphere 5.1. For example Commvault suggests not to use the VDDK 5.1 (click here for the Commvault documentation on this subject). Commvault advises to use VDDK 5.0 for vSphere 5.x. Veeam is not affected by the issue, see the comment of Doug Hazelman below. Veeam published a blogpost on the issue.
I would advise to investigate current support statements for your backup solution, especially in case you’re running vSphere 5.1.
Update: Marcel van den Berg of up2v.nl also wrote an article about the subject.