Unusually low number of exports for 2.12 file systems #54
Description
Our latest file system is 2.12.2 based, and after compiling the latest lmt to work with it, we noticed something unusual. We knew approximately how many clients had this file system mounted, but the export count shown in ltop was significantly lower. We also noticed after upgrading all our clients to 2.12.2 that the export counts on our 2.10.5 file systems were also lower, but not as low as on our new 2.12.2 system.
After stopping all jobs on our 2.12.2 file system for another reason, we noticed that the export counts went down to 2 or 3. More research led us to this new 2.12 feature: https://jira.whamcloud.com/browse/LU-7236. Apparently Lustre 2.12 has a "connections on demand" feature so the number of exports now equals the number of "active" clients. In the past, we used this as an indicator of how many clients were mounted.
In retrospect it makes sense, but it took us a while to figure out what was going on. I don't know if it makes sense to do anything to highlight this difference from the ltop side, but if nothing else this issue can be closed and serve as a notice to future 2.12 users explaining the cause for the new ltop behavior.