Synology NAS: Error: An unexpected network error occurred. Failed to write data to the file

[sanath.g@infosys.com]

Hi I'm facing the exact issue, we are also using the Synology NAS as backup repository. The backup fails midway with below error.

3/4/2024 5:49:06 PM :: Processing DEM01HIST01 error: DEM01HIST01 : Backup failed. Failed to backup disk: WriteData failed: An unexpected network error occurred.
Failed to write data to the file [\\10.95.30.135\Nutanix Backup\DEM01HIST01_Backup_2\DEM01HIST01_Backup_2_2024-03-04T165049.vbk].
Failed to download disk 'cbcc93e5-d7f7-4ada-a227-6e42ad52c3c0'.


I have contacted support team and I received below response.

The error messages you've shared usually indicate that some unknown problem led to a sudden failure of the connection between the repository gateway (acting as Server Message Block client) and the SMB server (typically a NAS appliance).

To prevent the issues from happening in the future, if the repository share is located on a Windows server, it's generally recommended to create a Windows repository on that server instead of a CIFS (SMB) repository as using NAS as CIFS shared repository is not an ideal option due to unstable SMB connection. It is a lot more reliable to reconfigure it as iSCSI since it offers a lot more stable connection.

Can anyone elaborate more on the above statement? I don't have much knowledge of storage part, please explain in the simpler terms

[sanath.g@infosys.com]

Adding further to my previous message. The VM is hosted on Nutanix. I have shared the logs in support portal. You can review it from the case #07160513

[Mildur]

Hello Sanath

I moved both of your comments from the other topic to a new topic.
The error message indeed means that there was an issue with the connection between the gateway server and your Synology NAS.
Our general recommendations for using an SMB share as a repository:
- Make sure to put the gateway server as near as possible to the NAS device. Don't put the gateway server in site 1 and the NAS device in site 2. It will affect backup jobs if there is a slow connection between both sites.
- Schedule active full backups instead of synthetic full backups. Active full backups will require less data transferred between the gateway server and NAS device.

I don't know the exact model of your Synology NAS. But we also recommend against using SMB on "home user targeted NAS devices" for our products. SMB repository may not work reliable enough on such devices. What our customer support means, is that you should reconsider your backup repository design. iSCSI can work far more stable than SMB.

Create an iSCSI LUN on your Synology, connect it to a windows server and format it with NTFS or ReFS (for ReFS please check first if your Synology model is listed as supported by Microsoft).
ReFS would give you our Veeam FastClone capabilities. Spaceless and fast synthetic full backups.

Best,
Fabian

[Moebius]

...for ReFS please check first if your Synology model is listed as supported by Microsoft).

Hello Fabian. How can I tell from this link if that given model is supported for ReFS by Microsoft? It just shows which Windows server version is certified for the specified models.

[Mildur]

Hi Lucio

All ReFS supported configurations must use Windows Server Catalog certified hardware and meet application requirements.

My understanding from Microsoft's Windows Server catalog, if a Synology model is listed in the certified hardware catalog, it is also supported by Windows with ReFS.

Best,
Fabian