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Date:      Sat, 10 Feb 2018 19:50:28 +0100
From:      Willem Jan Withagen <wjw@digiware.nl>
To:        Alan Somers <asomers@freebsd.org>
Cc:        freebsd current <freebsd-current@freebsd.org>
Subject:   Re: posix_fallocate on ZFS
Message-ID:  <985b6d77-9f27-f6f4-ea0e-165951d91048@digiware.nl>
In-Reply-To: <CAOtMX2jZr_kvJgOZWeiB-AZ3-7-uUu%2BUQ3P0nKhGZ0eNRzwMOQ@mail.gmail.com>
References:  <1e2f43fd-85da-6629-62d1-6e96790278e5@digiware.nl> <CAOtMX2jZr_kvJgOZWeiB-AZ3-7-uUu%2BUQ3P0nKhGZ0eNRzwMOQ@mail.gmail.com>

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On 10/02/2018 19:24, Alan Somers wrote:
> On Sat, Feb 10, 2018 at 10:28 AM, Willem Jan Withagen <wjw@digiware.nl 
> <mailto:wjw@digiware.nl>> wrote:
> 
>     Hi,
> 
>     This has been disabled on ZFS since last November.
>     And I do understand the rationale on this.
> 
>     BUT
> 
>     I've now upgraded some of my HEAD Ceph test systems and they now
>     fail, since Ceph uses posix_fallocate() to allocate space for the
>     FileStore-journal.
> 
>     Is there any expectation that this is going to fixed in any near future?
> 
>     --WjW
> 
> 
> No.  It's fundamentally impossible to support posix_fallocate on a COW 
> filesystem like ZFS.  Ceph should be taught to ignore an EINVAL result, 
> since the system call is merely advisory.

Yup, that was what I'm going to do.
But then I would like to know how to annotate it.

And I guess that I'd get reactions submitting code to fix this, since 
the journal could run out of space.
So I'd beter know what is going on.

I seem to remember that on a pool level is is possible to reserve space 
whilest creating a filesystem? And then it could/should be fixed when 
building the disk-infra for an OSD.

--WjW





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