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Re: [linux-lvm] cache buffer size



On Fri, Nov 08, 2002 at 09:11:42AM +0100, Luca Berra wrote:
> On Thu, Nov 07, 2002 at 05:58:01PM +0100, Heinz J . Mauelshagen wrote:
> >On Wed, Nov 06, 2002 at 11:17:05AM -0600, Steve Best wrote:
> >Indeed snapshot exception table ios go by blocks of 1k.
> >
> >Puting the snapshot store on the same device as the original is not
> >recommended in general for performance reasons.
> >
> >In case 1k blocks are possible with JFS:
> >
> >if snapshots are used regularly and there's no seperate PV to put the
> >snapshot onto, you might want to create a 1k blocked jfs and try if
> >that performs better than the RAID 5 stripe cache flush penalty with the 4k
> >blocked filesystem.
> 
> hello,
> is there any chance of having snapshots with 4k blocks for the exception
> table (configurable), i want to use snapshot for backing up my root vg
> but i also have swap there and it is locked to do page-sized io (4k on
> ix86).

I guess no, because the snapshot io block size is retrieved from
blksize_size[][] for the underlying physical volume.  Because of that we
have 1024 byte for the typical disk drive unless on zSeries.


> 
> L.
> 
> -- 
> Luca Berra -- bluca comedia it
>         Communication Media & Services S.r.l.
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-- 

Regards,
Heinz    -- The LVM Guy --

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***

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Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
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