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Date:   Wed, 12 Dec 2018 23:11:19 +0100 (CET)
From:   "Mkrtchyan, Tigran" <tigran.mkrtchyan@desy.de>
To:     ffilz@redhat.com
Cc:     linux-nfs <linux-nfs@vger.kernel.org>
Message-ID: <1207626803.5525544.1544652679619.JavaMail.zimbra@desy.de>
In-Reply-To: <378995dd-00b2-a2e8-fbee-025d4fc2eb24@redhat.com>
References: <043701d4925f$7b244530$716ccf90$@mindspring.com> <378995dd-00b2-a2e8-fbee-025d4fc2eb24@redhat.com>
Subject: Re: What is a reasonable minimum lease time?
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Thread-Topic: What is a reasonable minimum lease time?
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Hi Frank,

IMHO, very short leases can trigger a massive state recovery on network hiccups.

Our server offers 90 seconds to the client. The client usually renew lease (sequence) once in a minute.
During high IO periods lease is not required and when idle, then once in a minute is sufficient to
keep the mount alive. In a worst case, when a client got a lock and dispersal, a competing lock/open
will block only for 90s. Whatever number you have, it should be 


BTW, IETF mailing list probably a better place for this question.

Regards,
   Tigran.


----- Original Message -----
> From: "Frank Filz" <ffilz@redhat.com>
> To: "linux-nfs" <linux-nfs@vger.kernel.org>
> Sent: Wednesday, December 12, 2018 10:14:59 PM
> Subject: What is a reasonable minimum lease time?

> We have an issue with the Ganesha server with very short (2 second)
> lease times. Ganesha uses a 1 second granularity for lease management,
> and considers a time since last renewed equal to the lease time as too
> long. The result is that the lease period may be short close to 2
> seconds depending on when within a given second things actually happened
> (so a last renew at 0.99 with a subsequent renew at 2.01 which is just
> over one second looks like 2 seconds to Ganesha and thus is >= the 2
> second lease time and not good enough. A simple change would be to
> change the >= to a >, which gives one more second, but it still could
> result in the lease time being almost 1 second too short which is
> significant with a 2 second lease time. But if the minimum reasonable
> lease time is more like 5 or 10 seconds, that 1 second becomes less
> significant.
> 
> The bigger fix would be to use a finer grained time, but that adds
> complexity, but if people really want to run with 2 second lease times
> and it makes any kind of sense, we would need to make that change.
> 
> Thanks
> 
> 
> Frank