Unless this changed in 2.6 the block devices go through VFS, and the blocks get 
cached by the VFS layer.

-----Original Message-----
From: Linux on 390 Port [mailto:[EMAIL PROTECTED] Behalf Of
Mark Perry
Sent: Thursday, August 21, 2008 11:07 PM
To: [email protected]
Subject: Re: Root filesystem error switches to ReadOnly


Fargusson.Alan wrote:
> Doing a dd on a device goes through the cache, so in this case the cache 
> can't be the problem.

Really?

dd is designed to work on block devices that are not mounted, as well as
files within a mounted filesystem.

I thought the VFS only cached mounted filesystems?

If the dd is using something like "if=/dev/dasda of=dev/dasdb" then I
would have thought that the cache would not be used. The cache is only
used for mounted filesystems, i.e. files/blocks referenced within the FS
via the mountpoint.

mark

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