Resolve "Update troubleshooting for gzip error in backup docs"

doc/raketasks/backup_restore.md

@@ -960,3 +960,22 @@ want to run the chown against your custom location instead of
 
 [reconfigure GitLab]: ../administration/restart_gitlab.md#omnibus-gitlab-reconfigure
 [restart GitLab]: ../administration/restart_gitlab.md#installations-from-source
+
+### Backup fails to complete with Gzip error
+
+While running the backup, you may receive a gzip error:
+
+```sh
+sudo /opt/gitlab/bin/gitlab-rake gitlab:backup:create
+Dumping ...
+...
+gzip: stdout: Input/output error
+
+Backup failed
+```
+
+If this happens, check the following:
+
+1. Confirm there is sufficent diskspace for the gzip operation.
+1. If NFS is being used, check if the mount option `timeo` is set. The default is `600`, and changing this to smaller values have resulted in this error.
+