[Lustre-devel] Start the MGS first?

[Lustre-devel] Start the MGS first?

[Nathaniel Rutman]

As of Lustre 1.6, servers can be started in any order (after the initial registration at first startup).  Internally, this required significant bending of our connection rules, and with a move toward ZFS becomes even more burdensome.  
So my question to the Lustre community is this: would anyone strenuously object to a startup ordering requirement that the MGS must be started before any other servers?  
This would probably be in the Lustre 3.0 timeframe.  It is also likely that we will have to divorce the MGS and MDT onto separate devices -- no more "combo" MDT/MGSes. 

> >  NR> I think the only reason to have a local config file is to be able to
> >  NR> start a server in the absence of the MGS.  How much effort do we want
> >  NR> to expend to be able to keep that ability?  I don't think it's a huge
> >  NR> burden to say "MGS must be started first".

[Lustre-devel] Start the MGS first?

[Brian J. Murrell]

On Wed, 2009-03-25 at 12:48 -0700, Nathaniel Rutman wrote:
> As of Lustre 1.6, servers can be started in any order (after the initial registration at first startup).  Internally, this required significant bending of our connection rules, and with a move toward ZFS becomes even more burdensome.  
> So my question to the Lustre community is this: would anyone strenuously object to a startup ordering requirement that the MGS must be started before any other servers?  
> This would probably be in the Lustre 3.0 timeframe.  It is also likely that we will have to divorce the MGS and MDT onto separate devices -- no more "combo" MDT/MGSes. 

I'll ask before anyone else does... would this require the MGS be
available at any time a server (or client?) needs to start rather than
the optional behaviour (for anything but first time server starts) that
we currently enjoy?  IOW, does this make the MGS a much more critical
component of the filesystem than it is currently?

b.

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[Lustre-devel] Start the MGS first?

[Nicholas Henke]

Nathaniel Rutman wrote:
> As of Lustre 1.6, servers can be started in any order (after the initial 
> registration at first startup).  Internally, this required significant 
> bending of our connection rules, and with a move toward ZFS becomes even 
> more burdensome.  So my question to the Lustre community is this: would 
> anyone strenuously object to a startup ordering requirement that the MGS 
> must be started before any other servers?  This would probably be in the 
> Lustre 3.0 timeframe.  It is also likely that we will have to divorce 
> the MGS and MDT onto separate devices -- no more "combo" MDT/MGSes.
>> >  NR> I think the only reason to have a local config file is to be 
>> able to
>> >  NR> start a server in the absence of the MGS.  How much effort do 
>> we want
>> >  NR> to expend to be able to keep that ability?  I don't think it's 
>> a huge
>> >  NR> burden to say "MGS must be started first".
> 

This is virtually ensured today due to how the timeouts and ordering works.

1) It is a real PITA to script up different server start orders to deal with 
reformat and write_conf. It is easier to just script one correct way of doing 
this - KISS if you will.

2) At large scale, the timeout cascading on the OSTs (many OSTs per OSS) from a 
missing MGS requires it be started first.

3) With bug 14134 and --nomgs and --nosvc options for starting, it makes 
starting a combo MGS and MDS "correctly" much easier.

Nic

[Lustre-devel] [Lustre-discuss] Start the MGS first?

[Kevin Fox]

On Wed, 2009-03-25 at 12:48 -0700, Nathaniel Rutman wrote:
> As of Lustre 1.6, servers can be started in any order (after the
> initial registration at first startup).  Internally, this required
> significant bending of our connection rules, and with a move toward
> ZFS becomes even more burdensome. 
> So my question to the Lustre community is this: would anyone
> strenuously object to a startup ordering requirement that the MGS must
> be started before any other servers? 
> This would probably be in the Lustre 3.0 timeframe.  It is also likely
> that we will have to divorce the MGS and MDT onto separate devices --
> no more "combo" MDT/MGSes.
> 

"server startup" being, things wont start working until the MGS is up,
or, server startup commands will fail if the MGS is not up?

The former, is much better then the latter. It allows the system to
potentially bring itself back up automatically if things get rebooted
(power bump, spike, etc).

Kevin

> > >  NR> I think the only reason to have a local config file is to be
> able to
> > >  NR> start a server in the absence of the MGS.  How much effort do
> we want
> > >  NR> to expend to be able to keep that ability?  I don't think
> it's a huge
> > >  NR> burden to say "MGS must be started first".
> 
> 
> _______________________________________________
> Lustre-discuss mailing list
> Lustre-discuss at lists.lustre.org
> http://lists.lustre.org/mailman/listinfo/lustre-discuss
> 
> 

[Lustre-devel] Start the MGS first?

[Nathaniel Rutman]

Brian J. Murrell wrote:
> On Wed, 2009-03-25 at 12:48 -0700, Nathaniel Rutman wrote:
>   
>> As of Lustre 1.6, servers can be started in any order (after the initial registration at first startup).  Internally, this required significant bending of our connection rules, and with a move toward ZFS becomes even more burdensome.  
>> So my question to the Lustre community is this: would anyone strenuously object to a startup ordering requirement that the MGS must be started before any other servers?  
>> This would probably be in the Lustre 3.0 timeframe.  It is also likely that we will have to divorce the MGS and MDT onto separate devices -- no more "combo" MDT/MGSes. 
>>     
>
> I'll ask before anyone else does... would this require the MGS be
> available at any time a server (or client?) needs to start rather than
> the optional behaviour (for anything but first time server starts) that
> we currently enjoy?  IOW, does this make the MGS a much more critical
> component of the filesystem than it is currently?
>   
yes.    It's already required for client starts.  What we would do is 
have the MDT / OST server mounts block until the MGS is up, probably 
with a timeout.
And yes, this will be some amount less flexible than the current startup 
order, but we gain advantages from it - simplified import states, more 
centralized configuration, single-path disk access.  The question is how 
burdensome really will this limitation be.  So far I have not heard very 
much gnashing of teeth and rending of garments.

[Lustre-devel] [Lustre-discuss] Start the MGS first?

[Nathaniel Rutman]

Kevin Fox wrote:
> On Wed, 2009-03-25 at 12:48 -0700, Nathaniel Rutman wrote:
>   
>> As of Lustre 1.6, servers can be started in any order (after the
>> initial registration at first startup).  Internally, this required
>> significant bending of our connection rules, and with a move toward
>> ZFS becomes even more burdensome. 
>> So my question to the Lustre community is this: would anyone
>> strenuously object to a startup ordering requirement that the MGS must
>> be started before any other servers? 
>> This would probably be in the Lustre 3.0 timeframe.  It is also likely
>> that we will have to divorce the MGS and MDT onto separate devices --
>> no more "combo" MDT/MGSes.
>>
>>     
>
> "server startup" being, things wont start working until the MGS is up,
> or, server startup commands will fail if the MGS is not up?
>
> The former, is much better then the latter. It allows the system to
> potentially bring itself back up automatically if things get rebooted
> (power bump, spike, etc).
>
>   
The former.  Server mount commands would just block until the MGS was 
available (probably with an optional timeout).  So the only thing that 
would fail is serialized startup of OST before MGS -- independent, 
unordered startup would sort itself out.
> Kevin
>
>   
>>>>  NR> I think the only reason to have a local config file is to be
>>>>         
>> able to
>>     
>>>>  NR> start a server in the absence of the MGS.  How much effort do
>>>>         
>> we want
>>     
>>>>  NR> to expend to be able to keep that ability?  I don't think
>>>>         
>> it's a huge
>>     
>>>>  NR> burden to say "MGS must be started first".
>>>>         
>> _______________________________________________
>> Lustre-discuss mailing list
>> Lustre-discuss at lists.lustre.org
>> http://lists.lustre.org/mailman/listinfo/lustre-discuss
>>
>>
>>     
>
> _______________________________________________
> Lustre-devel mailing list
> Lustre-devel at lists.lustre.org
> http://lists.lustre.org/mailman/listinfo/lustre-devel
>