Proxmox modified vzdump-hook script, disable l2arc before backup and reenable it afterwards so not to trash the cache

vzdump-hook-script.pl.sh

#!/usr/bin/perl -w

# modified hook script, disable l2arc before backup and reenable it afterwards so not to trash the cache

use strict;

print "HOOK: " . join (' ', @ARGV) . "\n";

my $phase = shift;

if ($phase eq 'job-start' || 
    $phase eq 'job-end'  || 
    $phase eq 'job-abort') { 

    # dumpdir is not available with all backup-methods
    my $dumpdir = $ENV{DUMPDIR};
    # set the variable to empty string if it is undefined
    $dumpdir //= "";

    my $storeid = $ENV{STOREID};

    print "HOOK-ENV: dumpdir=$dumpdir;storeid=$storeid\n";

    # flush zfs async-memory before backup
    if ($phase eq 'job-start') {
		print "HOOK-ENV: ZFS disabling L2ARC ...\n";
			system ("/sbin/zfs set secondarycache=none rpool") == 0 ||
			die "zfs L2ARC disable failed!";
    }

    # flush zfs async-memory after backup
    if ($phase eq 'job-end') {
		print "HOOK-ENV: ZFS enabling L2ARC ...\n";
			system ("/sbin/zfs set secondarycache=all rpool") == 0 ||
			die "zfs L2ARC enable failed!";
    }

    # do what you want 

} elsif ($phase eq 'backup-start' || 
	 $phase eq 'backup-end' ||
	 $phase eq 'backup-abort' || 
	 $phase eq 'log-end' || 
	 $phase eq 'pre-stop' ||
	 $phase eq 'pre-restart' ||
	 $phase eq 'post-restart') {

    my $mode = shift; # stop/suspend/snapshot

    my $vmid = shift;

    my $vmtype = $ENV{VMTYPE}; # openvz/qemu

    # dumpdir is not available with all backup-methods
    my $dumpdir = $ENV{DUMPDIR};
    # set the variable to empty string if it is undefined
    $dumpdir //= "";

    my $storeid = $ENV{STOREID};

    my $hostname = $ENV{HOSTNAME};

    # tarfile is only available in phase 'backup-end'
    my $tarfile = $ENV{TARFILE};
    # set the variable to empty string if it is undefined
    $tarfile //= "";

    # logfile is only available in phase 'log-end'
    my $logfile = $ENV{LOGFILE}; 
    # set the variable to empty string if it is undefined
    $logfile //= "";

    print "HOOK-ENV: vmtype=$vmtype;dumpdir=$dumpdir;storeid=$storeid;hostname=$hostname;tarfile=$tarfile;logfile=$logfile\n";
    
} else {

    die "vzdump-hook-script.pl: got unknown phase '$phase'";

}

exit (0);

modify line 27 and line 34 to match your system.

activate the hook-script by default by editing the file /etc/vzdump.conf and adjusting the script parameter