Date: Wed, 10 Jul 2013 21:38:07 +0100 From: "Steven Hartland" <killing@multiplay.co.uk> To: "Justin T. Gibbs" <gibbs@FreeBSD.org> Cc: freebsd-fs@freebsd.org, =?iso-8859-1?Q?Dag-Erling_Sm=F8rgrav?= <des@des.no>, d@delphij.net, ivoras@freebsd.org, freebsd-hackers@freebsd.org Subject: Re: Make ZFS use the physical sector size when computing initial ashift Message-ID: <BA9B5EB953C34512BC7F9410507619F1@multiplay.co.uk> References: <86zjtupz3r.fsf@nine.des.no> <51DD9801.4090808@delphij.net> <2B9367B6-8759-45C9-B120-9D00A381228F@FreeBSD.org> <97E5A0A8DFBF4F75AAE8EDEFDF849EB0@multiplay.co.uk> <0A3A05F7-7859-4285-B15A-5E7DDB751062@FreeBSD.org> <7BB4167807A4434A9CD5FB0F1600439F@multiplay.co.uk> <00205B20-742F-44F6-B538-3B809D8BC03F@FreeBSD.org>
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----- Original Message -----
From: "Justin T. Gibbs"
...
>>> > One issue I did spot in your patch is that you currently expose
>>> > zfs_max_auto_ashift as a sysctl but don't clamp its value which would
>>> > cause problems should a user configure values > 13.
>>>
>>> I would expect the zio pipeline to simply insert an ashift aligned thunking
>>> buffer for these operations, but I haven't tried going past an ashift of 13 in
>>> my tests. If it is an issue, it seems the restriction should be based on
>>> logical access size, not optimal access size.
>>
>> Yes with your methodology you'll only see the issue if zfs_max_auto_ashift
>> and physical_ashift are both > 13, but this can be the case for example
>> on a RAID controller with large stripsize.
>
> I'm not sure I follow. logical_ashift is available in our latest code, as is the
> physical_ashift. But even without the logical_ashift, why doesn't the zio
> pipeline properly thunk zio_phys_read() access based on the configured ashift?
When I looked at it, which was a long time ago now so please excuse me if
I'm a little rusty on the details, zio_phys_read() was working more luck than
judgement as the offsets passed in where calculated from a valid start + increment
based on the size of a structure within vdev_label_offset() with no ashift
logic applied that I cound find.
The result was pools created with large ashift's where unstable when I
tested.
Regards
Steve
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