Port of ZFSOnLinux solution for illumos-gate issue #2663 to FreeBSD

[Steven Hartland]

----- Original Message ----- 
From: "Richard Yao" <ryao at gentoo.org>
>> Teach ZFS about geom stripe size so zpools are created with optimum ashift
>> http://www.freebsd.org/cgi/query-pr.cgi?pr=173115
>>
>> I've got an updated patch which allows the min ashift to be configured.
>>
>> It should be noted that the max working ashift appears to be 17
>> due the way labels use zio_read_phys with offset.
>
> Your patch modifies autodetection while this patch provides a manual
> override. They should be able to co-exist.

Yes indeed that was my intention :)

> With that said, the orignal patch permitted ashift=17, but that was
> shown to permit pool corruption:
>
> https://github.com/zfsonlinux/zfs/issues/425
>
> As far as I know, ashift=13 is the highest value permitted on both Linux
> and FreeBSD. The code can operate with higher values, but I do not
> recommend them.

Interesting I'll have a play with that there may be other edge cases I'm
not aware of thanks for the heads up.

    Regards
    Steve

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