This will extract the id & label from each block much more quickly than your code, by reading one block at a time. I didn't understand your hash, so I've left that to you.

#! perl -slw
use strict;
use Data::Dump qw[ pp ];

$/ = "\n----"; ## read 1 multiline record at a time

while( <DATA> ) {
    my( $label, $id ) = m[
        -El \s+ (\S+) .+?
        serial_id \s+ ( \S+ )
    ]xms or die 'Bad data';

    print "$label : $id";

}

__DATA__
---- lsattr -El vgbkup ----
auto_on       y                                N/A True
conc_auto_on  n                                N/A True
conc_capable  n                                N/A True
gbl_pbufs_ppv 0                                N/A True
gbl_pbufs_pvg 0                                N/A True
timestamp     49188ced308665bd                 N/A True
vg_pbufs_ppv  0                                N/A True
vgserial_id   00c0b42000004c000000011a5f8b013e N/A False
---- lsattr -El vgfrd01 ----
auto_on       y                                N/A True
conc_auto_on  n                                N/A True
conc_capable  n                                N/A True
gbl_pbufs_ppv 0                                N/A True
gbl_pbufs_pvg 0                                N/A True
timestamp     4ae7197814a6d91a                 N/A True
vg_pbufs_ppv  0                                N/A True
vgserial_id   00c0b42000004c000000011a0d27a4bc N/A False
---- lsattr -El loglv02 ----
copies       1                                  N/A True
inter        m                                  N/A True
intra        m                                  N/A True
label        None                               N/A True
lvserial_id  00c0b42000004c000000011a5f8b013e.2 N/A False
relocatable  y                                  N/A True
size         1                                  N/A True
strictness   y                                  N/A True
stripe_size                                     N/A True
stripe_width 0                                  N/A True
type         jfs2log                            N/A True
upperbound   64                                 N/A True
---- lsattr -El lvbackup ----
copies       1                                  N/A True
inter        x                                  N/A True
intra        im                                 N/A True
label        /backup                            N/A True
lvserial_id  00c0b42000004c000000011a5f8b013e.1 N/A False
relocatable  y                                  N/A True
size         1200                               N/A True
strictness   y                                  N/A True
stripe_size                                     N/A True
stripe_width 0                                  N/A True
type         jfs2                               N/A True
upperbound   64                                 N/A True
[download]