RFC: making gpart default

Peter Wemm peter at wemm.org
Mon Dec 1 16:05:40 PST 2008


On Sat, Nov 29, 2008 at 7:30 PM, Marcel Moolenaar <xcllnt at mac.com> wrote:
>
> On Nov 29, 2008, at 1:56 PM, Peter Wemm wrote:
[..]
>> * There should be some guidance or hints on laying out disks.  For
>> example,  a gpart create -s gpt on a raid volume ends up with a start
>> sector of 34 for the free space.  There should be a documentation hint
>> to round up start sectors to a power of 2 and/or block size on a raid.
>> eg: if you have a raid with 64K stripes, then move the start sector
>> from 34 to 128.  Otherwise  we end up with file systems issuing
>> transactions that can split across multiple raid stripes.  FWIW, I
>> conveniently filled this hole with boot code.
>
> Hmmm... gpart(8) typically can't store this kind
> of information on-disk, but other than that it
> supports alignment/padding already. We just need
> a way to tell gpart about it. Maybe this should
> come from the provider (i.e. underlying geom)...

I was more thinking of a man page note to warn of the issue.

Also, in the gpt case, it might make sense in gpt partition table case
to round up the initial size to a power of 2.  Right now we lose 34
sectors from the beginning.  Rounding it to 64 total at least gets us
to an even power of 2.  UFS's frequent block size of 16K shouldn't
cross any underlying stripe boundaries in the usual case.

-- 
Peter Wemm - peter at wemm.org; peter at FreeBSD.org; peter at yahoo-inc.com; KI6FJV
"All of this is for nothing if we don't go to the stars" - JMS/B5
"If Java had true garbage collection, most programs would delete
themselves upon execution." -- Robert Sewell


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