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Date:      Tue, 05 May 1998 12:16:58 -0700
From:      Julian Elischer <julian@whistle.com>
To:        Poul-Henning Kamp <phk@critter.freebsd.dk>
Cc:        Bruce Evans <bde@FreeBSD.ORG>, cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG, cvs-sys@FreeBSD.ORG
Subject:   Re: cvs commit: src/sys/kern vfs_cluster.c
Message-ID:  <354F65AA.41C67EA6@whistle.com>
References:  <2008.894388790@critter.freebsd.dk>

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Poul-Henning Kamp wrote:
> 
> It should really be a mount-option, shouldn't it ?

well, maybe more than that.
Is it really a question of whether the underlying device can 
handle a larger IO?

I'm not sure what the author of those bits had in mind when they 
added them. I'm thinking of adding the capacity in the SLICE code for
larger IO requests to be broken up transparently (ala physio())
(or possibly similar to ccd, (I'm not sure yet) 
or for a "report your capabilities" method which would report..
slice size
block size
optimum IO size
minimum IO size
Maximum IO size
? CLUSTER capabilities (as per this discussion)?


maybe both.

now that soft updates is slowing down I may have some time for
such niceties again.

> 
> Poul-Henning
> 
> In message <Pine.BSF.3.95.980501093134.1869G-100000@current1.whistle.com>, Juli
> an Elischer writes:
> >Talking of clusterring..
> >
> >One problem with clustering is the fact that the flag that dissallows
> >CLUSTERING is stored in the BDEVSW entry.
> >
> >from sys/conf.h:
> >#define D_NOCLUSTERR 0x10000 /* disables cluter read */
> >#define D_NOCLUSTERW 0x20000 /* disables cluster write */
> >#define D_NOCLUSTERRW (D_NOCLUSTERR | D_NOCLUSTERW)
> >
> > which is patently the wrong place for it. for several reasons:
> >
> >1/ different SCSI devices may have different ideas about clustering..
> >2/ in DEVFS/SLICE, all disks come in through the same major number/devfs[]
> >entry no matter which driver they eventually get passed to.
> >3/ [bc]devsw entries will totally go away anyhow.
> 
> --
> Poul-Henning Kamp             FreeBSD coreteam member
> phk@FreeBSD.ORG               "Real hackers run -current on their laptop."
> "ttyv0" -- What UNIX calls a $20K state-of-the-art, 3D, hi-res color terminal

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