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Answers inline.<br>
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<div class="moz-cite-prefix">On 12/29/2017 01:10 AM, Omar Kohl
wrote:<br>
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<pre wrap="">Hi,
I know that "glusterbot" text about ping-timeout almost by heart by now ;-) I have searched the complete IRC logs and Mailing list from the last 4 or 5 years for anything related to ping-timeout.</pre>
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I have to laugh, because I'm the one that wrote that text and I have
to use glusterbot to remember it. :D<br>
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The problem with "can be a very expensive operation" is that this is extremely vague. It would be helpful to put some numbers behind it. Of course I also understand that any numbers would be very case specific and would not necessarily generalize to other use cases. So anyway...
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It is vague, I agree. When I first started using gluster it was
huge. It would take over half an hour of high server load and slow
fops (30% of normal) after a ping-timeout for our servers with about
5000 open FDs. It would be so slow that the ping packets would get
delayed for sometimes 30 seconds. If the ping-timeout had been
shorter than that, this would have caused the whole process to start
all over again.<br>
<br>
I haven't had the time or the use case to look at whether or not
that's been mitigated at all in more recent versions. I suspect at
least some of it has.<br>
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Coming back to my original problem: If a Microsoft Windows client mounts a Samba Share with an underlying Gluster volume and this volume goes away for more than 25 seconds then the Samba Share is dead and any file operation is cancelled. This means for instance that a big file that is being copied will be stored in an incomplete state in the Gluster volume. This is especially annoying since one server (Gluster brick) is online the whole time and all operations could in theory have continued without problems.</pre>
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If the fop is cancelled, the application should get an error and the
application <i>should</i> handle that error to prevent data loss.
That's POSIX. Having this happen once every couple of years should
be within expectations (if it's not, expectations should be managed
better, imho).<br>
<br>
As an aside, I can't find 25 seconds in the Samba source. Are you
sure? Do you have some sort of log message to track this down with?<br>
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If I reduce the ping-timeout to something like 5 seconds the problem goes away! File operations in the Samba Share will stall for a few seconds and then everything will continue.
I understand that with a regular server shutdown this should never happen anyway. In practice (at least with CentOS 7) this does still happen (possibly because the network goes away too quickly, as you suggested) but it should be fixable. BUT I definitely want to support hard server crashes as well. The current behaviour of the Samba Share is not an option!
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Yeah, I'd be curious what's killing the network. It shouldn't be
killed at all. NetworkManager? I know that systemd-networkd doesn't
break this.<br>
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Would you therefore say it is appropriate in my use case to decrease the ping-timeout? Or can you think of anything else that could/should be done? I have no control over the client.
Since there are plenty of layers that everything goes through there are many reasons that additional delays could be caused. So my first instinct would be to reduce ping-timeout as much as possible to avoid coming near those "25 seconds". Therefore my question on some specific data of what the "ping-timeout" costs are.</pre>
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I won't go so far as to say it's appropriate. If you know and test
all the variables around changing a setting, it's your system and if
you trust your own judgement for your use case who am I to
second-guess. Since I first started trying to change it and failed,
I've taken the approach of fixing any other problems that might get
in the way of leaving it at 42 seconds. I've not been required to
change the ping-timeout in any of <i>my</i> production clusters.<br>
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What confirms me in my belief that 42 seconds ping-timeout for a Samba share is not appropriate is the script from the Gluster repository I linked to in a previous mail:
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<pre wrap="">I found the extras/hook-scripts/start/post/S29CTDBsetup.sh script that mounts a CTDB (Samba) share and explicitly sets the ping-timeout to 10 seconds. There is a comment saying: "Make sure ping-timeout is not default for CTDB volume". Unfortunately there is no explanation in the script, in the commit or in the Gerrit review history (<a class="moz-txt-link-freetext" href="https://review.gluster.org/#/c/7569/">https://review.gluster.org/#/c/7569/</a>, <a class="moz-txt-link-freetext" href="https://review.gluster.org/#/c/8007/">https://review.gluster.org/#/c/8007/</a>) for WHY you make sure ping-timeout is not default. Can anyone tell me the reason?
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I've CC'd Harsha to see if he has any feedback on that. He's off
working on Minio now, but maybe he remembers or has an opinion.<br>
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Thanks for your help!
Kind regards,
Omar
-----Ursprüngliche Nachricht-----
Von: Joe Julian [<a class="moz-txt-link-freetext" href="mailto:joe@julianfamily.org">mailto:joe@julianfamily.org</a>]
Gesendet: Freitag, 29. Dezember 2017 06:35
An: Sam McLeod <a class="moz-txt-link-rfc2396E" href="mailto:mailinglists@smcleod.net"><mailinglists@smcleod.net></a>
Cc: Gluster Users <a class="moz-txt-link-rfc2396E" href="mailto:gluster-users@gluster.org"><gluster-users@gluster.org></a>; Omar Kohl <a class="moz-txt-link-rfc2396E" href="mailto:omar.kohl@iternity.com"><omar.kohl@iternity.com></a>
Betreff: Re: [Gluster-users] Exact purpose of network.ping-timeout
Restarts will go through a shutdown process. As long as the network isn't actively unconfigured before the final kill, the tcp connection will be shutdown and there will be no wait.
On 12/28/17 20:19, Sam McLeod wrote:
Sure, if you never restart / autoscale anything and if your use case isn't bothered with up to 42 seconds of downtime, for us - 42 seconds is a really long time for something like a patient management system to refuse file attachments from being uploaded etc...
We apply a strict patching policy for security and kernel updates, we often also load balance between underlying physical hosts and if the virtual hosts have lots of storage it can be quicker to let them shutdown and start on another host.
So for us, gone are the old Unix days of caring about uptime, a huge part of our measurement of success and risk reduction has become how quickly we can not just deploy our software / web apps into production but also how quickly our platform can be reformed, patched and migrated as is effective.
So in reality, I'd probably rolling restart our three node gluster clusters every few weeks or so depending on what patches have been released etc...
--
Sam McLeod
<a class="moz-txt-link-freetext" href="https://smcleod.net">https://smcleod.net</a>
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On 29 Dec 2017, at 11:08 am, Joe Julian <<a class="moz-txt-link-abbreviated" href="mailto:joe@julianfamily.org">joe@julianfamily.org</a> <a class="moz-txt-link-rfc2396E" href="mailto:joe@julianfamily.org"><mailto:joe@julianfamily.org></a> > wrote:
The reason for the long (42 second) ping-timeout is because re-establishing fd's and locks can be a very expensive operation. With an average MTBF of 45000 hours for a server, even just a replica 2 would result in a 42 second MTTR every 2.6 years, or 6 nines of uptime.
On December 27, 2017 3:17:01 AM PST, Omar Kohl <<a class="moz-txt-link-abbreviated" href="mailto:omar.kohl@iternity.com">omar.kohl@iternity.com</a> <a class="moz-txt-link-rfc2396E" href="mailto:omar.kohl@iternity.com"><mailto:omar.kohl@iternity.com></a> > wrote:
Hi,
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.
Exactly! ONLY 10 seconds instead of the default 42 seconds :-)
As I said before the problem with the 42 seconds is that a Windows Samba Client will disconnect (and therefore interrupt any read/write operation) after waiting for about 25 seconds. So 42 seconds is too high. In this case it would therefore make more sense to reduce the ping-timeout, right?
Has anyone done any performance measurements on what the implications of a low ping-timeout are? What are the costs of "triggering heals all the time"?
On a related note I found the extras/hook-scripts/start/post/S29CTDBsetup.sh <a class="moz-txt-link-rfc2396E" href="http://s29ctdbsetup.sh/"><http://s29ctdbsetup.sh/></a> script that mounts a CTDB (Samba) share and explicitly sets the ping-timeout to 10 seconds. There is a comment saying: "Make sure ping-timeout is not default for CTDB volume". Unfortunately there is no explanation in the script, in the commit or in the Gerrit review history (<a class="moz-txt-link-freetext" href="https://review.gluster.org/#/c/7569/">https://review.gluster.org/#/c/7569/</a>, <a class="moz-txt-link-freetext" href="https://review.gluster.org/#/c/8007/">https://review.gluster.org/#/c/8007/</a>) for WHY you make sure ping-timeout is not default. Can anyone tell me the reason?
Kind regards,
Omar
-----Ursprüngliche Nachricht-----
Von: <a class="moz-txt-link-abbreviated" href="mailto:gluster-users-bounces@gluster.org">gluster-users-bounces@gluster.org</a> <a class="moz-txt-link-rfc2396E" href="mailto:gluster-users-bounces@gluster.org"><mailto:gluster-users-bounces@gluster.org></a> [<a class="moz-txt-link-freetext" href="mailto:gluster-users-bounces@gluster.org">mailto:gluster-users-bounces@gluster.org</a>] Im Auftrag von <a class="moz-txt-link-abbreviated" href="mailto:lemonnierk@ulrar.net">lemonnierk@ulrar.net</a> <a class="moz-txt-link-rfc2396E" href="mailto:lemonnierk@ulrar.net"><mailto:lemonnierk@ulrar.net></a>
Gesendet: Dienstag, 26. Dezember 2017 22:05
An: <a class="moz-txt-link-abbreviated" href="mailto:gluster-users@gluster.org">gluster-users@gluster.org</a> <a class="moz-txt-link-rfc2396E" href="mailto:gluster-users@gluster.org"><mailto:gluster-users@gluster.org></a>
Betreff: Re: [Gluster-users] Exact purpose of network.ping <a class="moz-txt-link-rfc2396E" href="http://network.ping/"><http://network.ping/></a> -timeout
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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