Date: Wed, 23 Jan 2013 14:16:29 -0000 From: "Steven Hartland" <killing@multiplay.co.uk> To: "Peter Jeremy" <peter@rulingia.com>, "Michael DeMan" <freebsd@deman.com> Cc: FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Re: RFC: Suggesting ZFS "best practices" in FreeBSD Message-ID: <32D3BF4572C74ED49F6978A16E340FE2@multiplay.co.uk> References: <314B600D-E8E6-4300-B60F-33D5FA5A39CF@sarenet.es> <AAE9CC17-B5C4-43DC-B86B-2F498FCA5AD4@deman.com> <20130123111852.GM30633@server.rulingia.com>
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----- Original Message -----
From: "Peter Jeremy" <peter@rulingia.com>
On 2013-Jan-22 17:27:13 -0800, Michael DeMan <freebsd@deman.com> wrote:
>>I could be disinformed here, but my understanding) is best practice is
>> to use gpart + gnop to:
>>#1. Ensure proper alignment for 4K sector drives - the latest western
>> digitals still report as 512.
>
> Recent versions of ZFS allow you to specify ashift=12 without needing
> gnop. And in any case, gnop is only needed when you initialise the
> pool. Once the initial ashift value is set, it can't be changed.
> (And I'd be interested in knowing how well a SSD ZIL compensates for
> having an ashift=9 pool on 4K sector disks).
I'm not aware of any other option to specify ashift in current sources.
I have outstanding patches which add auto alignment detection for disks
which report 4K either native or via quirks to ZFS. In addition it provides
the ability to set a default min ashift which essentially provides an
override.
This works well for us but the implemention details, which uses stripsize,
are under discussion with pjd and avg.
Regards
Steve
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