I' trying to develop Mongodb filesystem snapshots.

I have 2 filesystems (XFS)

• /mongodb (main dir)

• /database (one database on a separate filesystem - for performace, symlinked at /mongodb/database)

I tried scenario decribed at https://docs.mongodb.com/manual/tutorial/backup-with-filesystem-snapshots/:

1) db.fsyncLock()

2) tar /mongodb

3) tar /database

4) db.fsyncUnlock()

All is done on a 4th node of reaplica set, that is :

"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : true,
"priority" : 0,
"tags" : {},
"slaveDelay" : NumberLong(0),
"votes" : 1

I discovered, that even after running db.fsyncLock() (and 100% ensured it is active by running db.CurrentOp() ), tar command complains about files in /database being changed at doing backup. Modification times of a complained files are a log after db.fsyncLock() was executed, so tar is right about those files changed. I also see some writes to this /database filesystem at the time tar was running (by watching dstat output)

I'm I missing something here?

Best regards

Piotr Rybicki