Short code, using a (relatively) complex regex with negative look-ahead for the special case "unassigned": 
use strict;
use warnings;

local $/="\narray ";
while (<DATA>){
    s/\n(?!unassigned)(:?array)?/ /g;
    print  my $row=(m/^array/?"":"array "). "$_\n";
}
__DATA__
array A
physicaldrive 2C:1:1 port 2C:box 1:bay 1 SAS 1 TB OK
physicaldrive 2C:1:2 port 2C:box 1:bay 2 SAS 1 TB OK
array B
... etc ...
unassigned
physicaldrive 7C:3:7 port 7C:box 3:bay 7 SAS 1 TB OK
...

[download]
Output : 
array A physicaldrive 2C:1:1 port 2C:box 1:bay 1 SAS 1 TB OK physicald
+rive 2C:1:2 port 2C:box 1:bay 2 SAS 1 TB OK  
array B physicaldrive 2C:1:3 port 2C:box 1:bay 3 SAS 1 TB OK physicald
+rive 2C:1:4 port 2C:box 1:bay 4 SAS 1 TB OK  
... 
array J physicaldrive 6C:3:3 port 6C:box 3:bay 3 SAS 1 TB OK physicald
+rive 6C:3:4 port 6C:box 3:bay 4 SAS 1 TB OK  
array K physicaldrive 7C:3:5 port 7C:box 3:bay 5 SAS 1 TB OK physicald
+rive 7C:3:6 port 7C:box 3:bay 6 SAS 1 TB OK
unassigned physicaldrive 7C:3:7 port 7C:box 3:bay 7 SAS 1 TB OK physic
+aldrive 7C:3:8 port 7C:box 3:bay 8 SAS 1 TB OK

[download]
Separating the "unassigned" in $row is left as an exercise.

        "You're only given one little spark of madness. You mustn't lose it."         - Robin Williams

In reply to Re: Join multiple lines in a string based on regex. by NetWallah
in thread Join multiple lines in a string based on regex. by pr33

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