cbbackupmgr restore is taking a long time on build 7.1.0-1515

In our daily run with build 7.1.0-1515, we saw the restore process was taking a long time to finish. The run hit the timeout threshold and was aborted.

http://perf.jenkins.couchbase.com/job/triton_analytics/1806/ 

08:08:18 Running: ./opt/couchbase/bin/cbbackupmgr restore

11:01:14 Transferri... at 7.76MiB/s (about 1h41m41s remaining) 202626905 items / 78.47GiB

11:01:14 [============================================ ] 62.95%

11:01:14 Build timed out (after 180 minutes). Marking the build as aborted.

http://perf.jenkins.couchbase.com/job/triton_analytics/1810/
https://s3.amazonaws.com/bugdb/jira/qe/collectinfo-2021-10-18T202807-ns_1%40triton-srv-01-ip6.perf.couchbase.com.zip
https://s3.amazonaws.com/bugdb/jira/qe/collectinfo-2021-10-18T202807-ns_1%40triton-srv-02-ip6.perf.couchbase.com.zip
https://s3.amazonaws.com/bugdb/jira/qe/collectinfo-2021-10-18T202807-ns_1%40triton-srv-03-ip6.perf.couchbase.com.zip
https://s3.amazonaws.com/bugdb/jira/qe/collectinfo-2021-10-18T202807-ns_1%40triton-srv-04-ip6.perf.couchbase.com.zip
https://s3.amazonaws.com/bugdb/jira/qe/collectinfo-2021-10-18T202807-ns_1%40triton-srv-05-ip6.perf.couchbase.com.zip
https://s3.amazonaws.com/bugdb/jira/qe/collectinfo-2021-10-18T202807-ns_1%40triton-srv-06-ip6.perf.couchbase.com.zip
 

The last good run we have was running on build 7.1.0-1504. In this run, it took about 40 minutes to finish the restore process. 

http://perf.jenkins.couchbase.com/job/triton_analytics/1804/

08:09:19 [INFO] Running: ./opt/couchbase/bin/cbbackupmgr restore

08:47:31 Restore completed successfully