Don't rely on the behaviour of SSMS, which has historically been buggy or poorly documented and also sometimes changes from version to version.
The easiest way to be sure is to click the "script" button on top of the dialog and compare the output to the documentation.
For example when you click the script button after adding several files in the SSMS ...
Well let's just go ahead and test it...
Back Up Database - StackExchange
Added multiple file in the Backup Properties' General Tab
We'll add a comment to inform other of what we were trying to achieve.
Script Out The Backup
Just so we know what SSMS does in the background we'll script out the settings and run the script ...
with cte as
( select distinct trim(regexp_substr('1:30,2:4,52:0,8:1,90:54', '[^,]+', 1, level)) repfield,
connect by regexp_substr('1:30,2:4,52:0,8:1,90:54', '[^,]+', 1, level) is not null
order by lvl)
SUBSTR(repfield,1,instr(repfield , ':')-1) AS Field1,
SUBSTR(repfield,instr(repfield,':')+1,length(repfield)) as ...
Using SSMS to create multiple backup files will stripe the backup across those files, rather than duplicating the backup onto each file.
This means that each file is also needed for the restore - if you only keep one you'll only have a part of the data set.
Any speedup in a striped backup will come from using multiple IO channels. If all the files are in the same storage location it won't be any faster.
Using multiple CPU cores to process a backup probably won't help, as backup is extremely simple. And a single CPU core can saturate the storage subsystem with backup pages.
You can see this for yourself with ...
Splitting to separate fields of a result set is a bit tricky if you have a varying number of elements per row. There is a SQLCLR stored procedure in the SQL# library (that I wrote) that, while not in the Free version, does break a delimited string of varying elements into result set fields based on a Regular Expression delimiter. The delimiter being RegEx ...
This is also not pretty, but it allows for as\many\sub\folders\as\you\may\have.
-- borrowing from Brent:
CREATE TABLE #Files (Parentpath varchar(100), Size int);
INSERT INTO #Files (Parentpath, Size)
VALUES ('Business\Packets\Data\Archive', 29334),
DECLARE @s char(1) = CHAR(92), @sql nvarchar(max) =...