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If  you need to find out which process is doing io on your Linux server maybe these steps help to find the process.

• First  Save  this  Script as  "iodump"

#!/usr/bin/env perl

=pod

=head1 NAME

iodump - Compute per-PID I/O stats for Linux when iotop/pidstat/iopp are not available.

=head1 SYNOPSIS

Prepare the system:

dmesg -c
/etc/init.d/klogd stop
echo 1 > /proc/sys/vm/block_dump

Start the reporting:

while true; do sleep 1; dmesg -c; done | perl iodump
CTRL-C

Stop the system from dumping these messages:

echo 0 > /proc/sys/vm/block_dump
/etc/init.d/klogd start

=head1 LICENSE

This software is released to the public domain, with no guarantees whatsoever.

=cut

use strict;
use warnings FATAL => 'all';
use English qw(-no_match_vars);
use sigtrap qw(handler finish untrapped normal-signals);

my %tasks;

my $oktorun = 1;
my $line;
while ( $oktorun && (defined ($line = <>)) ) {
my ( $task, $pid, $activity, $where, $device );
( $task, $pid, $activity, $where, $device )
= $line =~ m/(\S+)\((\d+)\): (READ|WRITE) block (\d+) on (\S+)/;
if ( !$task ) {
( $task, $pid, $activity, $where, $device )
= $line =~ m/(\S+)\((\d+)\): (dirtied) inode \(.*?\) (\d+) on (\S+)/;
}
if ( $task ) {
my $s = $tasks{$pid} ||= { pid => $pid, task => $task };
++$s->{lc $activity};
++$s->{activity};
++$s->{devices}->{$device};
}
}

printf("%-15s %10s %10s %10s %10s %10s %s\n",
qw(TASK PID TOTAL READ WRITE DIRTY DEVICES));
foreach my $task (
reverse sort { $a->{activity} <=> $b->{activity} } values %tasks
) {
printf("%-15s %10d %10d %10d %10d %10d %s\n",
$task->{task}, $task->{pid},
($task->{'activity'}  || 0),
($task->{'read'}      || 0),
($task->{'write'}     || 0),
($task->{'dirty'}     || 0),
join(', ', keys %{$task->{devices}}));
}

sub finish {
my ( $signal ) = @_;
if ( $oktorun ) {
print STDERR "# Caught SIG$signal.\n";
$oktorun = 0;
}
else {
print STDERR "# Exiting on SIG$signal.\n";
exit(1);
}
}

• Then turn on kernel messages  about I/O:

#echo 1 > /proc/sys/vm/block_dump

• This makes the kernel start writing messages about every I/O operation that takes place. Now all you have to do is get those messages and feed them into the iodump script:

# while true; do sleep 1; dmesg -c; done | perl iodump
^C# Caught SIGINT.
TASK                   PID      TOTAL       READ      WRITE      DIRTY DEVICES
firefox               4450       4538        251       4287          0 sda4, sda3
kjournald             2100        551          0        551          0 sda4
firefox              28452        185        185          0          0 sda4
kjournald              782         59          0         59          0 sda3
pdflush                 31         30          0         30          0 sda4, sda3
syslogd               2485          2          0          2          0 sda3
firefox              28414          2          2          0          0 sda4, sda3

• When finished, turn off kernel messages about I/O:

#echo 0 > /proc/sys/vm/block_dump