+1 NFSv3 has always been more stable in our testing..

Will have to put it on the road map to run full testing again, but you know the old adage, if it ain't broke, don't fix it.. ;)

On 2023-05-19 08:23, Adrian Minta wrote:

Hi Pierre,

when we tested NFSv4 couple of years ago,  we found out that NFSv4 has a caching feature witch delegate file caching to a specific client. This was a problem with same share mounted on multiple servers. The contention will explode the load on the clients due to I/O waits and in some cases crash the dovecot servers.

We didn't use dovecot director at that time since NFSv3 was behaving more nicely and just worked on our tests.

It seem that some NFSv4 flags exists and could mitigate this behaviour making it resemble NFSv3 but we didn't test them.

On 5/19/23 17:21, pierre.alletru@gmail.com wrote:

...

Hi Dovecot community,

We're looking at running multiple Dovecot backend servers in parallel, all using the same shared NFSv4.1 mount to store mailboxes in the maildir format.

We've read in multiple places that running multiple backends with a shared NFS can result in issues like index files corruption. The standard solution seems to use the Director feature, or some kind of IP based proxy/load balancer.

But: 1 - The Director feature will be removed in future free versions of Dovecot (https://dovecot.org/mailman3/archives/list/dovecot@dovecot.org/thread/ILA3C6...). 2 - NFSv4 and above support file locking (flock and fcntl, flock being emulated using fcntl). 3 - It looks like Dovecot does use file locking, though we're unsure if it does on everything and in particular on index files.

Thus, we are wondering if the need for Director is still relevant with NFSv4? Shouldn't it work without Director thanks to file locking? Has anyone tried it? We're thinking that the documentation and various threads on the subject may be outdated, based on NFSv3 and lower (no file locking).

If it doesn't work, anybody knows why? Isn't file locking there precisely to handle concurrency?

Thanks!

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On 20/05/2023 01:23, Adrian Minta wrote:

Hi Pierre,

when we tested NFSv4 couple of years ago, we found out that NFSv4 has a caching feature witch delegate file caching to a specific client. This was a problem with same share mounted on multiple servers. The contention will explode the load on the clients due to I/O waits and in some cases crash the dovecot servers.

We didn't use dovecot director at that time since NFSv3 was behaving more nicely and just worked on our tests.

It seem that some NFSv4 flags exists and could mitigate this behaviour making it resemble NFSv3 but we didn't test them.

NFSv4, a dozen front ends to an EMC backend, with v4 we added "noac lookupcache=none" in very early days - not sure if they are still needed.

otherwise just like when using NFSv3, no problems, and never used director. real (hardware) load balancers are actually smart and exponentially more reliable and robust than server based :)

-- Regards, Noel Butler

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Nice to know, similar option doesn't exist on VNX's though

On 22/05/2023 17:30, Adrian M wrote:

On EMC Unity there is a NAS server parameter that can be changed to disable NFSv4 delegations using the following command, svc_nas -param -facility nfsv4 -modify delegationsEnabled -value 0

On Sun, May 21, 2023 at 7:34 AM Noel Butler noel.butler@ausics.net wrote:

...

NFSv4, a dozen front ends to an EMC backend, with v4 we added "noac lookupcache=none" in very early days - not sure if they are still needed.

otherwise just like when using NFSv3, no problems, and never used director. real (hardware) load balancers are actually smart and exponentially more reliable and robust than server based :)

-- Regards, Noel Butler

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On 22/05/2023 22:33, Marc wrote:

...

used director. real (hardware) load balancers are actually smart and exponentially more reliable and robust than server based :) because there runs no software on it, right ....

this statement here, shows what a clueless newbie you are

-- Regards, Noel Butler

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On 22/05/2023 22:36, Marc wrote:

...

On EMC Unity there is a NAS server parameter that can be changed to

Maybe a bit to much of topic, but why EMC and not something like ceph? You rarely see any interesting comparisons on line (except of course the stupid ones listing features)

there is a reason these things cost more than you'll earn in a year.

second post in a row showing your lack of knowledge in actual networks,
before you make an even bigger ass out of yourself, how about getting some experience in the real world or spending some time researching from actual information - not blogs

-- Regards, Noel Butler

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On 23/05/2023 17:23, Marc wrote:

there is a reason these things cost more than you'll earn in a year.

second post in a row showing your lack of knowledge in actual networks, before you make an even bigger ass out of yourself, how about getting some experience in the real world or spending some time researching from actual information - not blogs

Since when has there ever been a relationship between money and being good, money and intelligence etc. 2nd I have a hard time

welcome to reality, time for you to jump back in your short narrow minded bubble if thats your beliefs.

believing that are still companies out there that hardwire millions of logic circuits to create a load balancer that meets current day standards without the use of any software, and the

perhaps open your dark curtains some day, but since when do companies have to explain shit to a troll like you explaining why they do things the way they do.

Noel the only dumb ass here seems to be you. You are certainly not a good advocate for the EMC product compared to institutions like NASA and CERN that have >4000 drives in ceph solutions.

oh I hope your happy, I'm gonna lose a lot of sleep over that piss poor pathetic attempt to disparage me . n o t ... better people have tried and failed over the past 30 years.

final words, I don't care how nasa cern or whoever run their network, christ, i'm not even in the same country as them so why would I care, and the fact they have a name that most, but not all, would recognise, means nothing, Microsoft is a big name too, as is google, bigger and more known, and they have made some monumental fuck ups. I get it your a fangirl, and you can never reason with people like you.

the end.

On 05/06/2023 20:52, Eirik Rye wrote:

On 05/06/2023 11:14, Noel Butler via dovecot wrote:

...

[...]

Both of you should grow up and keep this argument outside the mailing list.

yes mum

Thanks Tom. Are you refering to a proxy software in particular (e.g. Dovecot proxy, Nginx, ...)? Do you mean having a single proxy in front of all the backends?

We'd prefer to avoid that if possible, as that makes the proxy a single point of failure. But it seems to be the recommended way to deal with cluster indeed (https://doc.dovecot.org/configuration_manual/nfs/#clustering-without-directo...).