Re: mon disk access pattern

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On Fri, 15 Jun 2012, Mark Nelson wrote:
> On 06/15/2012 04:51 AM, Wido den Hollander wrote:
> > Hi,
> > 
> > On 15-06-12 07:52, Stefan Priebe - Profihost AG wrote:
> > > Hello list,
> > > 
> > > i read somewhere that the mon has "special" disk access patterns - even
> > > though it does not write much data.
> > 
> > "special"? Where did you read that? The monitor has about 1 ~ 2GB of
> > storage.
> > 
> > So if your monitor has something like 4GB ~ 8GB of RAM, your kernel
> > should cache almost all your monitor data.
> > 
> 
> I think at some point someone mentioned to me that the mon can cause a lot of
> syncs, so running them on the OSDs without syncfs might be detrimental.  For
> the majority of our internal performance testing I've kept them off the OSDs
> just to be sure.

Right.  The only thing interesting about the mon access pattern is that it 
calls fsync() a lot when healthy, and will call syncfs() or sync() during 
recovery.

sage
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