i have "奶過野 twice" after upgrading to 4.3.4 previous and current build. 431P2 created hundreds of files in duplicates after routine backup using freefilesync (a very stable file copy software). Even the QTS File Station was unable to delete those duplicates! Those files were "dead" within the system! It was deemed a kind of system crash. The only way to fix the problem, was to remove and recreate the Volume! And I did that ... twice! Luckily I am using 431P2 for backup only.
I am also using Synology 216+II (running DSM 6.1). While ppl (including qnap) saying how bad the btrfs is, as per my personal experience, it is far more stable than QTS 4.3.4 ext4!
"最怕是file crash, 但你又唔知。然後當你做下次做offline backup 時,overwrite 原本冇問題的file 咁就 hihi 啦"
Well, this was most likely a kind of 'file crash'!
"因為我做offline backup 會 "delete extra file in target folder"
Yes, I am using mirror mode. Will delete extra files in target folder!
The incident
17/03/2018 : Applied QTS 4.3.4.0516 build 20180315
18/03/2018 (02:00) : Scheduled daily backup using freefilesync (mirror mode with verify on) on Windows client machine. To copy files from 216+II to 431P2.
18/03/2018 early in the morning : Discovered hundreds of files in duplicates! Even QTS File Station was unable to remove those files!
I've been using freefilesync for years on various machines (including 216+II running Btrfs), the software itself should not be a problem.
Files in duplicates (QTS File Station screen capture)
Regarding file backup (with whatever tool we use), CRC check / Verify on must be enabled! And I will check the backup log thereafter. Otherwise ... hihi