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Date: Fri, 29 Oct 2004 11:06:33 -0700 (PDT)
From: Don Lewis <truckman@FreeBSD.org>
To: phk@critter.freebsd.dk
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Subject: Re: HEADSUP:  UFS on GEOM now.
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On 29 Oct, Poul-Henning Kamp wrote:
> 
> This is hopefully a no-op for all purposes than the increased access
> flexibility.
> 
> I am very interested if anybody can measure the performance difference
> better than I could myself:  1.7% +/- 0.5%.
> 
> Poul-Henning
> 
> phk         2004-10-29 10:15:56 UTC
> 
>   FreeBSD src repository
> 
>   Modified files:
>     sys/ufs/ffs          ffs_alloc.c ffs_extern.h ffs_rawread.c 
>                          ffs_snapshot.c ffs_softdep.c ffs_vfsops.c 
>                          ffs_vnops.c 
>     sys/ufs/ufs          inode.h ufs_vnops.c ufsmount.h 
>   Log:
>   Move UFS from DEVFS backing to GEOM backing.
>   
>   This eliminates a bunch of vnode overhead (approx 1-2 % speed
>   improvement) and gives us more control over the access to the storage
>   device.
>   
>   Access counts on the underlying device are not correctly tracked and
>   therefore it is possible to read-only mount the same disk device multiple
>   times:
>           syv# mount -p
>           /dev/md0        /var    ufs rw  2 2
>           /dev/ad0        /mnt    ufs ro  1 1
>           /dev/ad0        /mnt2   ufs ro  1 1
>           /dev/ad0        /mnt3   ufs ro  1 1
>   
>   Since UFS/FFS is not a synchrousely consistent filesystem (ie: it caches
>   things in RAM) this is not possible with read-write mounts, and the system
>   will correctly reject this.

Very cool!