Re: [ANNOUNCE] Ramback: faster than a speeding bullet

[Lars Marowsky-Bree]

On 2008-03-10T09:37:37, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:

> Why - your chunks simply become a linked list in write barrier order.
> Solve your bitmap sweep cost as well. As you are already making a copy
> before going to backing store you don't have the internal consistency
> problems of further writes during the I/O.

You get duplicated blocks though. But yes, I agree - write-backs to the
disk must be ordered, other it's going to be too unreliable in practice.

An in-memory buffer for a log-structured block device.

> Yes you may need to throttle in the specific case of having too many
> copies of pages sitting in the queue - but surely that would be the set of
> pages that are written but not yet committed from a previous store
> barrier ?

You could switch from a journal like the above to a bitmap when this
overrun occurs. (Typical problem in replication.) SteelEye holds a
patent on that though, as far as I know.


Regards,
    Lars

-- 
Teamlead Kernel, SuSE Labs, Research and Development
SUSE LINUX Products GmbH, GF: Markus Rex, HRB 16746 (AG Nürnberg)
"Experience is the name everyone gives to their mistakes." -- Oscar Wilde

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