Library Update / Refresh settings Advice Pls

I have read the wiki but i am struggling to work out correct config for me.
Looking for some advice and explaining my understanding on way..
http://wiki.serviio.org/doku.php?id=pc5dczc_console_explained

My collection is 20tb,
I regularly add/remove content from my movie folders but i never ammend existing content attributes/metadata.
I regularly add/remove content from my music folders and i rarely ammend existing content attributes/metadata. (happy to have to rely on a manual process if this is resource intensive on a 500GB library)
(FWIW: i dont intend to transcode anything.)

The relevant library settings are
scan for additions and updates - i need additions for movies and music but i dont think i need updates (certainly not on video)...so i have switched on for movies and music
search for updates of shared files - ideally i would have updates for music but i dont want 19.5tb scanned for movie updates when i never update...so i have switch off
keep library automatically updated - this i understand to be the 'master switch' that affects whether the above two settings are invoked 'automatically' or 'manually' - so i have this switched on.

pause between refreshes ...i dont understand yet....ive left on default of 10minutes....

Is my understanding correct that even if i force a refresh i wont get updates on music...and i cant force an update just for music?

2nd problem is, i reboot the pc and serviio starts 'aggressively' checking files....it doesnt seem to be just looking at date modified but invoking ffmpeg and using much server resources to 'deep check' every movie and music file....i havent asked for updates of shared files to prevent this...

the check in logs looks innocuuous...but serviio service is invoking ffmpeg...

  Code:

2012-11-05 10:44:06,242 DEBUG [MediaItemDAOImpl] Checking if DB already contains media item S02E21 - Apocalypse Wow!.avi
2012-11-05 10:44:06,242 DEBUG [MediaItemDAOImpl] Looking up a media item for file path: S:\TV1\This Life\Season 02\S02E21 - Apocalypse Wow!.avi, ignore case: true
2012-11-05 10:44:06,243 DEBUG [MediaItemDAOImpl] Media item S02E21 - Apocalypse Wow!.avi already exists in DB

Have i understood correctly...Have i got the correct config for me.

good to see that the checking/database process does seem robust..through service/pc restarts etc....other dlna servers fall over with the library too big.

[zip]

Is my understanding correct that even if i force a refresh i wont get updates on music...and i cant force an update just for music?

You will not get updates on the music/video metadata, eg new cover art, new title if you change the ID3 tag value, etc.

2nd problem is, i reboot the pc and serviio starts 'aggressively' checking files....it doesnt seem to be just looking at date modified but invoking ffmpeg and using much server resources to 'deep check' every movie and music file....i havent asked for updates of shared files to prevent this...

The log you posted is produced by the process that checks for additions/removals (your first point), so it's ok. It should not invoke FFmpeg, unless it adds new files though.