Date: Fri, 29 Jun 2007 19:34:56 +0000 From: Harry Newton <hn+freebsd@yewbarrow.net> To: Arne =?iso-8859-1?q?W=F6rner?= <arne_woerner@yahoo.com> Cc: freebsd-geom@freebsd.org Subject: Re: gmirror on a slice uncertainty Message-ID: <87fy4a1rmn.fsf@vm.yewbarrow.net> In-Reply-To: <186446.9762.qm@web30309.mail.mud.yahoo.com> (arne_woerner@yahoo.com's message of "Fri, 29 Jun 2007 07:46:33 -0700 (PDT)") References: <186446.9762.qm@web30309.mail.mud.yahoo.com>
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Arne - many thanks for your help. I've a couple more questions if you
don't mind ...
[...]
>> - this error message about partition c:
>> hydra# bsdlabel ad6s2
>> # /dev/ad6s2:
>> c: 583207694 0 unused 0 0 # "raw" part,
>> bsdlabel: partition c doesn't cover the whole unit!
>>
> see: ...694 (one sector less)
> This is because gmirror uses the last sector of the slice, so that the gmirror
> device (mirror/home) is one sector shorter than the slice...
[...]
I understand this now: gmirror reserves one sector for its metadata
(the last sector). I disklabel /dev/mirror/home which is one sector
smaller than the underlying disks. When I look at /dev/mirror/home
with bsdlabel there is no problem because the disklabel is consistent
with the size of the device (/dev/mirror/home). However, when I
report on the underlying disks with bsdlabel (which I can do because
they start at the same place) it notes the size discrepancy and issues
the warning.
I don't have to worry about that at all because I should be only
accessing through /dev/mirror/home.
>> - and this line in /var/log/messages:
>> WARNING: Expected rawoffset 0, found 41929650
>>
> 41929650 == 41929587+63
> This is the beginning of slice 2 (see fdisk)...
> I would guess, that slice 2 ends on the last sector of the disk, so that
> gmirror is disturbed (it doesnt know if ad4 or ad4s2 (which share both the same
> last sector) is its underlying disk)...
I haven't followed this. If I look at the disk with sysinstall:
Disk name: ad4 FDISK Partition Editor
DISK Geometry: 38913 cyls/255 heads/63 sectors = 625137345 sectors (305242MB)
Offset Size(ST) End Name PType Desc Subtype Flags
0 63 62 - 12 unused 0
63 41929587 41929649 ad4s1 8 freebsd 165
41929650 583207695 625137344 ad4s2 8 freebsd 165
625137345 5103 625142447 - 12 unused 0
I see there's space at the end of the disk. The code that produces the
message is in geom_bsd.c and is:
if (rawoffset != 0 && (off_t)rawoffset != ms->mbroffset)
printf("WARNING: Expected rawoffset %jd, found %jd\n",
(intmax_t)ms->mbroffset/dl.d_secsize,
(intmax_t)rawoffset/dl.d_secsize);
But I'm now confused as to what the importance of this message is ?
> You could solve that
> 1. by using hard coded disk names in gmirror
Is this to prevent ad4 and ad4s2 being confused ? Doesn't gmirror know
what the components that make up the provider are ?
[...]
> All errors/warnings r not so important possibly...
> I think ur gmirror device would work fine (but dont trust me without
> tests)...
I think you're probably right, but I'd like to do it right and
understand it more.
[...]
Thanks
- Harry
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