Date: Sun, 1 Jun 2014 17:00:21 +0100 From: "Steven Hartland" <killing@multiplay.co.uk> To: "Nathan Whitehorn" <nwhitehorn@freebsd.org>, <freebsd-hackers@freebsd.org>, <freebsd-fs@freebsd.org> Subject: Re: fdisk(8) vs gpart(8), and gnop Message-ID: <1DB2D63312CE439A96B23EAADFA9436E@multiplay.co.uk> 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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----- Original Message -----
From: "Nathan Whitehorn" <nwhitehorn@freebsd.org>
To: <freebsd-hackers@freebsd.org>; <freebsd-fs@freebsd.org>
Sent: Sunday, June 01, 2014 4:55 PM
Subject: Re: fdisk(8) vs gpart(8), and gnop
> 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.
>>
>> 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
I think you will get some objections to that, as it can have quite an impact
on the performance for disks which are 512, due to the increased overhead of
transfering 4k when only 512 is really required. This has a more dramatic
impact on RAIDZx due too.
Personally we run a custom kernel on our machines which has just this change
in it to ensure capability with future disks, so I can confirm it does indeed
have the desired effect :)
Regards
Steve
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