[Gluster-users] Exact purpose of network.ping-timeout

[lemonnierk at ulrar.net]

Hi,

It's just the delay for which a node can stop responding before being
marked as down.
Basically that's how long a node can go down before a heal becomes
necessary to bring it back.

If you set it to 10 seconds, and a node goes down, you'll see a 10
seconds freez in all I/O for the volume. That's why you don't want it
too high (having a 2 minutes freez on I/O for example would be
pretty bad, depending on what you host), but you don't want it too
low either (to avoid triggering heals all the time).

You can configure it because it depends on what you host. You might be
okay with a few minutes freez to avoid a heal, or you might not care
about heals at all and prefer a very low value to avoid feezes.
The default value should work pretty well for most things though

On Tue, Dec 26, 2017 at 01:11:48PM +0000, Omar Kohl wrote:
> Hi,
> 
> I have a question regarding the "ping-timeout" option. I have been researching its purpose for a few days and it is not completely clear to me. Especially that it is apparently strongly encouraged by the Gluster community not to change or at least decrease this value!
> 
> Assuming that I set ping-timeout to 10 seconds (instead of the default 42) this would mean that if I have a network outage of 11 seconds then Gluster internally would have to re-allocate some resources that it freed after the 10 seconds, correct? But apart from that there are no negative implications, are there? For instance if I'm copying files during the network outage then those files will continue copying after those 11 seconds.
> 
> This means that the only purpose of ping-timeout is to save those extra resources that are used by "short" network outages. Is that correct?
> 
> If I am confident that my network will not have many 11 second outages and if they do occur I am willing to incur those extra costs due to resource allocation is there any reason not to set ping-timeout to 10 seconds?
> 
> The problem I have with a long ping-timeout is that the Windows Samba Client disconnects after 25 seconds. So if one of the nodes of a Gluster cluster shuts down ungracefully then the Samba Client disconnects and the file that was being copied is incomplete on the server. These "costs" seem to be much higher than the potential costs of those Gluster resource re-allocations. But it is hard to estimate because there is not clear documentation what exactly those Gluster costs are.
> 
> In general I would be very interested in a comprehensive explanation of ping-timeout and the up- and downsides of setting high or low values for it.
> 
> Kinds regards,
> Omar
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