Re: [dm-crypt] Re: md-raid5, dm-crypt, alignment and readahead

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, Mar 12, 2008 at 12:47:02AM +0100, Christian Pernegger wrote:
> >  Is there a difference between running blockdev --setra and echo-int to
> >  /sys/block/.../read_ahead_kb for devices that have the entry in /sys?
> 
> To answer myself, blockdev --setra seems to change
> /sys/block/.../read_ahead_kb, so I'll just always use that.
> 
> >  How is readahead handled when "stacked" virtual block devices are
> >  involved?
> 
> Ran quite a few tests and readahead at any layer but the top layer did
> not have any effect. This means that read ahead blocks will always be
> decrypted. Oh well ...
>

Just to make it clear.. with "top layer" you mean you set read ahead only for
the dm-crypt device and NOT for the md-raid and/or physical sdX devices? 
 
-- Pasi
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