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DragonFly kernel List (threaded) for 2010-02
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Re: kernel work week of 3-Feb-2010 HEADS UP

From: Francois Tigeot <ftigeot@xxxxxxxxxxxx>
Date: Thu, 4 Feb 2010 18:06:41 +0100

On Wed, Feb 03, 2010 at 11:32:43AM -0800, Matthew Dillon wrote:
>     What I will be doing this week and possibly into next week is
>     implementing a system-wide cache-to-swap feature for objects backed
>     by the VM system.  Such objects include file data and filesystem
>     meta-data. The type of data/meta-data to cache will be selectable with
>     a sysctl and the write-bandwidth to the SSD will also be manageable.

That would be awesome :-)

Would it be possible to implement this as a multi-stage caching system ? Hard
drives come in 3 or 4 different speed grades these days and a caching layer
going from fastest drives to slow drives would make a lot of sense.

We could have this situation in a file server:

32 GB SSD  >  300GB in 15,000 RPM drives  >  10s of TB in 7200 RPM drives

Which is not too different from the multi-level caches of CPUs these days...

Francois Tigeot

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