Oracle RAC 11.2 with asm storage, all type = EXTERN redundancy.

I've been cleaning up some tablespaces and shrinking datafiles back down to sizes that they're not likely to grow much larger than (processes no longer used had blown them up).

The sum of the bytes of datafiles from dba_data_files reflects this shrink, however, USED_MB in v$asm_diskgroup has not fallen and it doesn't match to what adding up the datafiles bytes is?

What would account for this difference? We typically use v$asm_diskgroup to monitor if we're running low on space but this doesn't appear to be correct.

  SELECT name group_name ,
  type type ,
  total_mb total_mb ,
  (total_mb - free_mb) used_mb ,
  (SELECT SUM(bytes)/1024/1024
  FROM dba_data_files
  WHERE file_name LIKE '+DATA02%'
  ),0) AS datafile_used
FROM v$asm_diskgroup w
WHERE name = 'DATA02'

DATA02  EXTERN  542712  516902  506447
  • is this any help? prutser.wordpress.com/2013/01/03/…
    – Philᵀᴹ
    Commented Oct 27, 2016 at 14:41
  • @Philᵀᴹ - nope, because that mainly talks about the differences due to redundancy, which doesn't apply if TYPE = EXTERN
    – rfusca
    Commented Oct 27, 2016 at 15:15
  • Sometimes it takes a bit of time for USED_MB to catch up, in my experience. After 10 to 15 mins it shows the right values. Commented Oct 27, 2016 at 15:26
  • @AndrewBrennan - its been like 12+ hours
    – rfusca
    Commented Oct 27, 2016 at 16:28

1 Answer 1


dba_data_files does not include:

  • tempfiles
  • controlfiles
  • spfiles
  • redo logs
  • archived logs
  • backups/copies
  • ADVM volumes (ACFS)
  • OCR
  • reserved space for ASM metadata

Include v$asm_alias and v$asm_file in your queries, or just simply list the files in the diskgroup (asmcmd, ls).

  • If I go into asmcmd and ls the directory, its the exact same like from dba_data_files. That file group only has data files in it.
    – rfusca
    Commented Oct 27, 2016 at 15:14

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