Perhaps you could read all of the lines from your second file, before starting to process the first, and construct a single regular expression with all of the strings you want to exclude.

johngg@shiraz:~/perl/utils$ perl -Mstrict -Mwarnings -E '
open my $file2FH, q{<}, \ <<__EOD2__ or die $!;
/dumpx/DUMP4X/var/level6/55
/dumpx/DUMP4X/var/level7/58
__EOD2__

my $rxExcl = do {
   chomp( my @lines = <$file2FH> );
   local $" = q{|};
   qr{@lines};
   };

close $file2FH or die $!;

open my $file1FH, q{<}, \ <<__EOD1__ or die $!;
/dev/sda3 6 Fri Apr 12 04:27:19 2019 +0100   /dumpx/DUMP3X/var/level6/
+47    81.34 MB
/dev/sda4 6 Fri Apr 12 04:30:02 2019 +0100   /dumpx/DUMP4X/var/level6/
+55    86.53 MB
/dev/sdb1 6 Fri Apr 12 04:31:47 2019 +0100   /dumpx/DUMP4X/var/level6/
+56    27.73 MB
/dev/sdb2 6 Fri Apr 12 04:33:33 2019 +0100   /dumpx/DUMP4X/var/level7/
+58    57.32 MB
__EOD1__

while ( <$file1FH> )
{
    print unless m{$rxExcl};
}

close $file1FH or die $!;'
/dev/sda3 6 Fri Apr 12 04:27:19 2019 +0100   /dumpx/DUMP3X/var/level6/
+47    81.34 MB
/dev/sdb1 6 Fri Apr 12 04:31:47 2019 +0100   /dumpx/DUMP4X/var/level6/
+56    27.73 MB
[download]

I hope this is useful.