Avamar: VM Image backup takes longer to complete due to using nbd instead of hotadd

Summary: Avamar VM Image backup occasionally takes longer to complete due to using nbd instead of hotadd.

This article applies to This article does not apply to This article is not tied to any specific product. Not all product versions are identified in this article.
Check out other resources

Symptoms

An Avamar VMware image backup completion time is inconsistent.

Sometimes the backup completes quickly. 
2017-09-21 05:15:08 avtar Info <5156>: Backup #223 timestamp 2017-09-21 05:15:08, 0 files, 925.0 GB (0 files, 352.2 GB, 38.07% new)
2017-09-21 05:15:08 avtar Info <6083>: Backed-up 925.0 GB in 192.63 minutes: 288 GB/hour (0 files/hour)
2017-09-21 05:15:08 avtar Info <7883>: Finished at 2017-09-21 05:15:08 CEST, Elapsed time: 0003h:12m:37s

On 'slow' days, the backup takes much longer. The one below takes 24 hours. 
2017-09-23 02:10:04 avtar Info <5156>: Backup #224 timestamp 2017-09-23 02:10:04, 0 files, 925.0 GB (0 files, 334.5 GB, 36.16% new)
2017-09-23 02:10:04 avtar Info <6083>: Backed-up 925.0 GB in 1447.94 minutes: 38 GB/hour (0 files/hour)
2017-09-23 02:10:04 avtar Info <7883>: Finished at 2017-09-23 02:10:04 CEST, Elapsed time: 0024h:07m:56s

The backups have similar sizes and change rate. Both are running as 'synthetic full'. The logs indicate that the quicker backup is using 'hotadd' 
2017-09-21 02:03:06 avvcbimage Info <0000>: Connected with hotadd transport to virtual disk [XXXXX] XXXXXXXX.vmdk. Time to connect: 35082 msecs
The slower backup reports an issue connecting using hotadd. It falls back to using nbd. 
2017-09-22 02:13:22 avvcbimage Info <12006>: hotadd transport is recommended for faster backups and restores and less exposure to network routing, firewall and SSL certificate issues. 
2017-09-22 02:13:22 avvcbimage Info <12007>: One or more of these items may be preventing use of hotadd transport with this VM: 
2017-09-22 02:14:03 avvcbimage Info <12013>: Check that the VM being backed up is in the same datacenter as the backup proxy VM. Hotadd transport cannot cross a Datacenter boundary. . . . 
2017-09-22 02:13:22 avvcbimage Info <0000>: Connected with nbd transport to virtual disk [XXXXX] XXXXXXX.vmdk. Time to connect: 353256 msecs

Cause

On each day, the backup was using a different proxy.

Fast backup: 
2017-09-21 02:00:09 avvcbimage Info <18672>: proxy VM Instance name is: xxxxx-proxy-8 

Slower backup: 
2017-09-22 02:00:15 avvcbimage Info <18672>: proxy VM Instance name is: xxxxx-proxy-2 
The proxy used on 21st September was not available on 22nd September.
The backup used a different proxy, which had configuration problems.
When using this different proxy, it could not leverage the quicker 'hotadd' transport mode.

Resolution

The log recommends what to check if hotadd transport cannot be used.

If the VM configuration has not been altered, check on the proxy related configuration checks.
  
2017-09-22 02:13:22 avvcbimage Info <12007>: One or more of these items may be preventing use of hotadd transport with this VM:
2017-09-22 02:14:03 avvcbimage Info <12008>:  Check that the backup proxy VM(127.0.0.2,xxxx-avpro4,10.10.8.53,10.10.7.53) is deployed on an ESX(i) host that has a path to the storage holding the virtual disk being backed up ([XXXXXXXX] XXXXX.vmdk). Also check that the proxy is configured to protect this datastore
2017-09-22 02:14:03 avvcbimage Info <12009>:  Check that the vmfs holding the backup proxy VM has a total capacity equal to the size of the largest virtual disk being backed up. (Capacity merely has to be present - Free space can be less than this amount)
2017-09-22 02:14:03 avvcbimage Info <12010>:  Check that the vmfs holding the backup proxy VM is formatted with a vmfs block size which supports the size of the largest virtual disk being backed up
2017-09-22 02:14:03 avvcbimage Info <12011>:  Check that the VM being backed up has no virtual hard disks designated as independent
2017-09-22 02:14:03 avvcbimage Info <12012>:  Check that the VM being backed up has no IDE virtual hard disks, usually an artifact of a P2v conversion - use SCSI virtual disks instead
2017-09-22 02:14:03 avvcbimage Info <12013>:  Check that the VM being backed up is in the same datacenter as the backup proxy VM. Hotadd transport cannot cross a Datacenter boundary.
2017-09-22 02:14:03 avvcbimage Info <12014>:  Check that no VMs, and no vmdk's within the vCenter have the same name as those associated with the VM being backed up. (unusual but possible)

Affected Products

Avamar

Products

Avamar, Avamar Client for VMware
Article Properties
Article Number: 000046189
Article Type: Solution
Last Modified: 06 Feb 2025
Version:  6
Find answers to your questions from other Dell users
Support Services
Check if your device is covered by Support Services.