Re: [zfs-discuss] zfs periodic writes on idle system [Re: Getting desktop to auto sleep]

[Jürgen Keil]

 Why does zfs produce a batch of writes every 30 seconds on opensolaris b134
 (5 seconds on a post b142 kernel), when the system is idle?

It was caused by b134 gnome-terminal. I had an iostat
running in a gnome-terminal window, and the periodic
iostat output is written to a temporary file by gnome-terminal.
This kept the hdd busy. Older gnome-terminals (b111)
didn't write terminal output to a disk file. Workaround is
to use xterm instead of b134 gnome-terminal. for a
command that periodically produces output
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[zfs-discuss] zfs periodic writes on idle system [Re: Getting desktop to auto sleep]

[Jürgen Keil]

Why does zfs produce a batch of writes every 30 seconds on opensolaris b134
(5 seconds on a post b142 kernel), when the system is idle?

On an idle OpenSolaris 2009.06 (b111) system,  /usr/demo/dtrace/iosnoop.d
shows no i/o activity for at least 15 minutes.

The same dtrace test on an idle b134 system shows a batch of writes every 30 
seconds.

And on current opensolaris bits, on an idle system, I see writes every 5 
seconds.


The periodic writes prevents that the disk can enter power save mode.
And this breaks the /etc/power.conf autoS3 feature.  Why does zfs have
to write something to disk when the system is idle?



  Putting the flag does not seem to do anything to the
  system. Here is my power.conf file: 
 ...
  autopm  enable
  autoS3  enable
  S3-support  enable
 
 Problem seems to be that all power managed devices
 must be at their lowest power level, otherwise autoS3
 won't suspend the system.  And somehow one or more
 device does not reach the lowest power level.
...
 The laptop still does not power down, because every
 30 seconds there is a batch of writes to the hdd drive,
 apparently from zfs, and that keeps the hdd powered
 up.
 
 The periodic writes can be monitored with:
 
 dtrace -s /usr/demo/dtrace/iosnoop.d
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