Maintenance of small instrument restraining piano on record (6)
I believe the answer is:
upkeep
'maintenance' is the definition.
(synonyms)
'small instrument restraining piano on record' is the wordplay.
'small instrument' becomes 'uke' (short for ukulele; 'small' asks for a short form).
'restraining' is an insertion indicator.
'piano' becomes 'p' (musical abbreviation).
'on' says to put letters next to each other.
'record' becomes 'EP' (abbreviation for extended play record).
'uke' placed around 'p' is 'upke'.
'upke'+'ep'='UPKEEP'
'of' acts as a link.
(Other definitions for upkeep that I've seen before include "Cost of support" , "Looking after" , "Cost of maintaining" , "Running costs" , "Maintenance costs" .)