Is there a way to keep the 2.6 kjournald from writing to idle disks?(to allow spin-downs)

[Lutz Vieweg]

Hi everyone,

I run a server that usually doesn't have to do anything on the local filesystems,
it just needs to answer some requests and perform some computations in RAM.

So I use the "hdparm -S 123" parameter setting to keep the (IDE) system disk from
spinning unneccessarily.

Alas, since an upgrade to kernel 2.6 and ext3 filesystem, I cannot find a way to
let the harddisk spin down - I found out that "kjournald" writes a few blocks every
few seconds.

As I wouldn't like to downgrade to ext2: Is there any way to keep the 2.6 kjournald
from writing to idle disks?

I cannot see a good reason why kjournald would write when there are no dirty buffers -
but still it does.


Regards,

Lutz Vieweg


BTW: I used the following script to find the source of the write operations,
     just start it in one terminal, do a "sync" in another, then say "hdparm -y /dev/hda"
     and you can see that immediately or a few seconds later kjournald will enter the
     "D" state and wake up when the disk has spun up.

-------------------------------------------------------------------------------------
#!/usr/bin/tclsh

cd /proc


set stat_arr {
 pid
 comm
 state
 ppid
 process_group,
 session
 tty_nr
 tty_pgrp
 flags
 min_flt
 cmin_flt
 maj_flt
 cmaj_flt
 utime
 stime
 cutime
 cstime
 priority
 nice
 num_threads
 it_real_value
 start_time
 vsize
 rss
 RLIMIT_RSS
 start_code
 end_code
 start_stack
 esp
 eip
 pending_signals
 blocked_sigs
 sigign
 sigcatch
 wchan
 nswap
 cnswap
 exit_signal
 task_cpu
 rt_priorit
 policy
}

proc scan_stat {_pids _dat} {
   upvar $_dat dat
   upvar $_pids pids
   global stat_arr

   set pids [lsort -integer [glob {[0-9]*}]]

   foreach pid $pids {
           set in [open "$pid/stat" "r"]
           set l [gets $in]
           close $in

           set a [split $l " "]

           foreach x $a n $stat_arr {
                   set dat($pid,$n) $x
           }
   }
}

#puts [array get dat]

array set dat {}
set pids {}

scan_stat pids dat

while {1} {
        after 1000

        array set new_dat {}
        set new_pids {}

        scan_stat new_pids new_dat

        foreach pid $new_pids {
                if {$pid != [pid]} {
                   if {![info exists dat($pid,pid)]} {
                           puts "new process $pid $new_dat($pid,comm)"
                   } else {
                           set somechange 0
                           foreach a $stat_arr {
                                   if {$new_dat($pid,$a) != $dat($pid,$a)} {
                                           puts "$pid $new_dat($pid,comm) attribute '$a' from $dat($pid,$a) to 
$new_dat($pid,$a)"
                                           set somechange 1
                                   }
                           }
                           if {$somechange} {
                                   puts ""
                           }
                   }
                }
        }

        array set dat {}
        array set dat [array get new_dat]
        set pids $new_pids
}
-------------------------------------------------------------------------------------


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