I put some test data on the volume. Then after I have shutdown the NAS, I physically removed Drive 2 from the set. Then I turned the NAS back on. The NAS did turn on, but making a beeping sound. I could still log into the DSM 7.2 via the web interface, but it told me that one of the drive was missing -- as expected.
So what happened to the data? Unfortunately all the shares in the volume were inaccessible. They did not even show up in DSM File Station. I had hope that only the data in the removed drive would be missing, but the deleterious effect was global.
When I put Drive 2 back in, but removed Drive 1, the result was the same. All data was inaccessible. Basically, in a JBOD configuration, presumably applying to all Synology models with multi-drive configurations, the data is lost when one drive is removed or non-operational. This is the same effect as a RAID-0 set.
I had to rebuild the volume from scratch when a blank drive was put back into the storage pool.
