Backup or restore job hangs
NetBackup may have exceeded the maximum number of allowed VMware NFC connections to the ESX server when it used the transport modes nbd or nbdssl. Note that NetBackup uses one NFC connection per virtual disk on the ESX or ESXi server.
If NetBackup is configured to access the ESX server directly (not through a vCenter or VirtualCenter server), fewer connections are allowed. The following are the maximum connections as set by VMware:
Table: VMware NFC connection limits for nbd or nbdssl transfers
ESX version | Type of access to the ESX server | Maximum NFC connections allowed |
|---|---|---|
ESX 4 | Directly to ESX server | 9 |
ESX 4 | Through vCenter | 27 |
ESXi 4 | Directly to ESX server | 11 |
ESXi 4 | Through vCenter | 23 |
ESXi 5 | Directly to ESX server | The maximum total for all NFC connection buffers to an ESXi host is 32 MB |
ESXi 5 | Through vCenter | 52 |
Try a different transport type (such as SAN or hotadd). If a different transport type is not available and NetBackup accesses the ESX servers directly, set up access through a vCenter (or VirtualCenter) server. Use of a server increases the maximum number of allowed connections. For example: With 27 connections, NetBackup can access a virtual machine that has up to 27 disks, if the ESX 4 server is behind a vCenter server.
Note that the connection limits are per-host (that is, per vCenter or ESX server).
For example, assume the following environment:
An ESX 4.0 server with three virtual machines.
Each virtual machine has ten virtual disks.
The virtual machines are behind a vCenter 4.0 server.
For a simultaneous backup of the three virtual machines, NetBackup requires 30 NFC connections. With a limit of 27 NFC connections per vCenter server, any of the three backup jobs may hang.
These limits are described in the VMware Virtual Disk API Programming Guide:
VMware Virtual Disk API Programming Guide
See also the following section of the VMware vSphere 5 Documentation Center: