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Date:      Sun, 1 Jun 2014 14:31:52 -0700
From:      Matthew Ahrens <mahrens@delphix.com>
To:        Nathan Whitehorn <nwhitehorn@freebsd.org>
Cc:        freebsd-fs <freebsd-fs@freebsd.org>, FreeBSD Hackers <freebsd-hackers@freebsd.org>, George Wilson <george.wilson@delphix.com>
Subject:   Re: fdisk(8) vs gpart(8), and gnop
Message-ID:  <CAJjvXiHAvPptAUOg3aO35v32%2BF3VqG_8tNjgknOZ6qM1EeNK=w@mail.gmail.com>
In-Reply-To: <538B4CEF.2030801@freebsd.org>
References:  <20140601004242.GA97224@bewilderbeast.blackhelicopters.org> <CAOjFWZ5N9FGwgSz0_YFNQjavzdJDitRn52VKn4ipW1ddj6-weQ@mail.gmail.com> <BCA9F5D6-3925-4E7E-9082-128652508305@FreeBSD.org> <3D6974D83AE9495E890D9F3CA654FA94@multiplay.co.uk> <538B4CEF.2030801@freebsd.org>

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On Sun, Jun 1, 2014 at 8:55 AM, Nathan Whitehorn <nwhitehorn@freebsd.org>
wrote:

> On 06/01/14 08:52, Steven Hartland wrote:
>
>> ----- Original Message ----- From: "Mark Felder" <feld@freebsd.org>
>>
>>  On May 31, 2014, at 20:57, Freddie Cash <fjwcash@gmail.com> wrote:
>>>
>>>  There's a sysctl where you can set the minimum ashift for zfs. Then you
>>>> never need to use gnop.
>>>>
>>>> I believe it's part of 10.0?
>>>>
>>>
>>> I've not seen this yet. What we need is to port the ability to set
>>> ashift at pool creation time:
>>>
>>> $ zpool create -o ashift=12 tank mirror disk1 disk2 mirror disk3 disk4
>>>
>>> I believe the Linux zfs port has this functionality now, but we still do
>>> not.
>>>
>>
I am strongly against implementing "-o ashift=12"[*].  If we need to
explicitly tell ZFS what sector size to use, we should make that intention
clear with an appropriately named property, for example "-o
device_sector_size=4K".  Even better, this property should be per-disk.

--matt

[*]  Once we implement an appropriately-named property, I would be OK with
also allowing the "-o ashift=12" as a Linux compatibility feature.



>
>> We don't have that direct option yet but you can achieve the
>> same thing by setting: vfs.zfs.min_auto_ashift=12
>>
>>  Does anyone have any objections to me changing this default, right now,
> today?
> -Nathan
>
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