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Energy Saver Preferences Questions

I clearly do not understand these.  I have a computer that serves as a 
media server with the media on an attached external hard drive.  What I 
would like is for the computer to always be visible on the network but 
for it and the external drive to sleep when not in use.

I have the following settings:
	Computer Sleep - after 30 min
	Put Hard Drives(s) to sleep if possible - checked
	Wake for Etnernet network access - checked

What happens is that when the computer goes to sleep, it disappears 
from the network.  How can it "Wake for Ethernet network access" if it 
can't be seen?  I must be misunderstanding something.

The only way I can achieve network visibility is to have it (and 
presumably the attached external drive) not sleep at all.  I'm not 
worried about the energy consumption but about the heat generated and 
the wear on the disk and fan bearings.

Can someone please explain what the correct settings should be and what 
the point of "Wake for Ethernet network access" is?

-- 
Nelson

0
Nelson
12/23/2016 11:20:48 PM
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In article <0001HW.D4831B8002543D7EB02919BF@news.astraweb.com>, Nelson
<nelson@nowhere.com> wrote:

> What happens is that when the computer goes to sleep, it disappears 
> from the network. 

as expected.

> How can it "Wake for Ethernet network access" if it 
> can't be seen?  I must be misunderstanding something.

because you send the wake on lan packet to the ethernet mac address of
the computer, which then wakes the computer, at which point it becomes
visible on the network.
0
nospam
12/23/2016 11:45:03 PM
On 2016-12-23 23:20:48 +0000, Nelson <nelson@nowhere.com> said:

> The only way I can achieve network visibility is to have it (and
> presumably the attached external drive) not sleep at all.

The exception is if you are using an iTunes/Apple TV system, in which 
case the Apple TV will act as a Bonjour Sleep Proxy and it (and other 
Bonjour-capable devices) will continue to 'see' the instance of iTunes 
on the media server and can wake it up on demand.

A.

0
Alrescha
12/24/2016 12:33:59 AM
On 2016-12-23, Nelson <nelson@nowhere.com> wrote:
> I clearly do not understand these.  I have a computer that serves as a
> media server with the media on an attached external hard drive.  What
> I would like is for the computer to always be visible on the network
> but for it and the external drive to sleep when not in use.

A sleeping computer cannot respond to network requests.

> I have the following settings: Computer Sleep - after 30 min

Change that to None instead. You don't want the computer to sleep.

> 	Put Hard Drives(s) to sleep if possible - checked Wake for
> 	Etnernet network access - checked
>
> What happens is that when the computer goes to sleep, it disappears
> from the network.  How can it "Wake for Ethernet network access" if it
> can't be seen?  I must be misunderstanding something.

Enabling "Wake for Ethernet network access" enables the WOL (Wake On
LAN) feature, which listens for a very special "magic" packet on the
network port whenever the computer is sleeping or turned off. Unless
that special packet is sent by someone, the computer will ignore network
requests while sleeping:

<https://en.wikipedia.org/wiki/Wake-on-LAN>

So to use your computer the way you have it set up, you'd have to:

1. Refrain from making network requests to the computer whenever it is
sleeping.

2. Send the magic packet (typically by running an app that sends WOL
packets on another Mac or a smart phone) to wake up the computer.

3. Wait for the computer to wake up (maybe ping it while waiting or
something), and *then* send it whatever networks requests you are
making.

That's obviously not feasible as a long-term solution for a media
server. ; )

> The only way I can achieve network visibility is to have it (and
> presumably the attached external drive) not sleep at all.

The hard drive can sleep without issue (there will be a slight delay in
service whenever the file system needs access and the drive wakes up
from sleep, but that's about it); but the bottom line is the computer
must be *awake* to respond to network requests.

> I'm not worried about the energy consumption but about the heat
> generated and the wear on the disk and fan bearings.

Meh. Not worth the worry, IMO. I've had Macs running 24/7 for years
without any bearings going out. With hard drives, it's never a matter of
if, but rather *when* they will die. Having a solid backup regime is all
that is needed to be fully prepared for a hard drive failure.

-- 
E-mail sent to this address may be devoured by my ravenous SPAM filter.
I often ignore posts from Google. Use a real news client instead.

JR
0
Jolly
12/24/2016 2:14:33 AM
On 2016-12-23 18:20, Nelson wrote:

> What happens is that when the computer goes to sleep, it disappears 
> from the network.  How can it "Wake for Ethernet network access" if it 
> can't be seen?  I must be misunderstanding something.

The Ethernet card remains awake awake, but does not pass any packets to
the OS because the OS is asleep.  It still sees packets arriving from
the cable, but does nothing with them UNLESS a special packet is
received (the wake on LAN packlet which is a layer 2 packet (not IP)
adressed to the MAC address of that ethernet interface. When received,
the ethernet card sends a signal to the OS to wake up.


0
JF
12/24/2016 3:07:28 AM
In message <0001HW.D4831B8002543D7EB02919BF@news.astraweb.com> 
  Nelson <nelson@nowhere.com> wrote:
> I clearly do not understand these.  I have a computer that serves as a 
> media server with the media on an attached external hard drive.  What I 
> would like is for the computer to always be visible on the network but 
> for it and the external drive to sleep when not in use.

> I have the following settings:
> 	Computer Sleep - after 30 min
> 	Put Hard Drives(s) to sleep if possible - checked
> 	Wake for Etnernet network access - checked

> What happens is that when the computer goes to sleep, it disappears 
> from the network.  How can it "Wake for Ethernet network access" if it 
> can't be seen?  I must be misunderstanding something.

You have to send a special "Wake on LAN" packet to the machine.

<https://developer.apple.com/reference/localauthentication>

> The only way I can achieve network visibility is to have it (and 
> presumably the attached external drive) not sleep at all.  I'm not 
> worried about the energy consumption but about the heat generated and 
> the wear on the disk and fan bearings.

Computers are much happier constantly running. Turn off sleep for any
server and all will be good.

> Can someone please explain what the correct settings should be and what 
> the point of "Wake for Ethernet network access" is?

ARD will send WOL packets, as will Screen Sharing, I believe. A lot of
network scanners will also send WOL packets (like fing and nmap or
MochaWOL on iOS). There are also plenty of little MacOS apps that will
craft eh packet and send it for you. Should be easy to find Google "WOL
MacOS app"

-- 
Incredible! One of the worst performances of my career and they never
doubted it for a second.
0
Lewis
12/24/2016 5:47:20 AM
On 2016-12-23 22:07, JF Mezei wrote:
> On 2016-12-23 18:20, Nelson wrote:
>
>> What happens is that when the computer goes to sleep, it disappears
>> from the network.  How can it "Wake for Ethernet network access" if it
>> can't be seen?  I must be misunderstanding something.
>
> The Ethernet card remains awake awake, but does not pass any packets to
> the OS because the OS is asleep.  It still sees packets arriving from
> the cable, but does nothing with them UNLESS a special packet is
> received (the wake on LAN packlet which is a layer 2 packet (not IP)
> adressed to the MAC address of that ethernet interface. When received,
> the ethernet card sends a signal to the OS to wake up.

The OS is not running.  It can't receive signals to wake up.  The CPU 
sleep state controller receives the wake signal.  The CPU then begins 
running at a particular vector that is of course linked to the OS. 
Depending on the "depth" of sleep various context needs to be returned 
to the CPU (registers etc).

-- 
"If war is God's way of teaching Americans geography, then
recession is His way of teaching everyone a little economics."
   ..Raj Patel, The Value of Nothing.
0
Alan
12/24/2016 3:29:40 PM
In message <t4CdnUPC74j4CcPFnZ2dnUU7-VXNnZ2d@giganews.com> 
  Alan Browne <alan.browne@freelunchvideotron.ca> wrote:
> On 2016-12-23 22:07, JF Mezei wrote:
>> On 2016-12-23 18:20, Nelson wrote:
>>
>>> What happens is that when the computer goes to sleep, it disappears
>>> from the network.  How can it "Wake for Ethernet network access" if it
>>> can't be seen?  I must be misunderstanding something.
>>
>> The Ethernet card remains awake awake, but does not pass any packets to
>> the OS because the OS is asleep.  It still sees packets arriving from
>> the cable, but does nothing with them UNLESS a special packet is
>> received (the wake on LAN packlet which is a layer 2 packet (not IP)
>> adressed to the MAC address of that ethernet interface. When received,
>> the ethernet card sends a signal to the OS to wake up.

> The OS is not running.  It can't receive signals to wake up.

Read better. No one ever said that it did.

> The CPU sleep state controller receives the wake signal.

No. The Ethernet interface (or wifi chip) receives the WOL packet. How it
wakes up the machine at that point is entirely beyond the scope of WOL
and depends entirely on the hardware.

-- 
Spontaneity has its time and place.
0
Lewis
12/24/2016 7:18:44 PM
On 2016-12-24 14:18, Lewis wrote:
> In message <t4CdnUPC74j4CcPFnZ2dnUU7-VXNnZ2d@giganews.com>
>   Alan Browne <alan.browne@freelunchvideotron.ca> wrote:
>> On 2016-12-23 22:07, JF Mezei wrote:
>>> On 2016-12-23 18:20, Nelson wrote:
>>>
>>>> What happens is that when the computer goes to sleep, it disappears
>>>> from the network.  How can it "Wake for Ethernet network access" if it
>>>> can't be seen?  I must be misunderstanding something.
>>>
>>> The Ethernet card remains awake awake, but does not pass any packets to
>>> the OS because the OS is asleep.  It still sees packets arriving from
>>> the cable, but does nothing with them UNLESS a special packet is
>>> received (the wake on LAN packlet which is a layer 2 packet (not IP)
>>> adressed to the MAC address of that ethernet interface. When received,
>>> the ethernet card sends a signal to the OS to wake up.    <------------[1]
>
>> The OS is not running.  It can't receive signals to wake up.
>
> Read better. No one ever said that it did.

You read better.  See [1] above that Mezei wrote.  The Ethernet card 
does not "wake" the OS.  It sends a signal to the CPU to restore the 
state of the CPU. Thence the OS can restore its states and so on.

>
>> The CPU sleep state controller receives the wake signal.
>
> No. The Ethernet interface (or wifi chip) receives the WOL packet. How it
> wakes up the machine at that point is entirely beyond the scope of WOL
> and depends entirely on the hardware.

Which, as I pointed out and you snipped, hits the CPU long before the OS 
is aware of anything - which is what I was clarifying to JF.

-- 
"If war is God's way of teaching Americans geography, then
recession is His way of teaching everyone a little economics."
   ..Raj Patel, The Value of Nothing.
0
Alan
12/24/2016 9:49:16 PM
Reply: