Re: write-behind has no measurable effect?

[Roberto Spadim <roberto@spadim.com.br>]

andras could you make some benchmarks to raid1 with round robin read balance?
at this site:
www.spadim.com.br/raid1/

it's kernel 2.6.37 based


2011/2/15 Roberto Spadim <roberto@spadim.com.br>
>
> andras could you make some benchmarks to raid1 with round robin read balance?
> at this site:
> www.spadim.com.br/raid1/
>
> it's kernel 2.6.37 based
>
> 2011/2/14 Andras Korn <korn@raidlist.elan.rulez.org>
>>
>> On Tue, Feb 15, 2011 at 01:19:33AM +0000, John Robinson wrote:
>>
>> > >Another approach to take would be to mark as dirty, on the fast devices, all
>> > >areas being written to, and in the background continuously synch them to the
>> > >slow devices, sequentially (marking as clean synched-and-as-yet-unwritten-to
>> > >areas); so that the array would be resyncing continually, but be very fast
>> > >for random writes. This would of course also require the bitmap to only be
>> > >synchronously updated on the fast devices.
>> > >
>> > >Otoh, this is really a different mechanism from the current write-behind,
>> > >aimed at a different use-case, so maybe it could be implemented
>> > >orthogonally. (Patches welcome, I'm sure; it's times like these I hate not
>> > >being a coder.)
>> >
>> > I wonder whether bcache might do roughly what you want? I haven't
>>
>> It only does very roughly what I want (the idea there is to _cache_ a much
>> larger spinning disk using a relatively small SSD, whereas I basically want
>> them both to be the same size, with the disk eventually mirroring the
>> contents of the SSD); also, development of bcache has stalled (it doesn't
>> even compile with recent kernels and the developer has stated that he's
>> taking a break).
>>
>> I also know of flashcache, which is similar to bcache and is more actively
>> developed, but is still lagging quite a few versions behind (the latest
>> kernel it works with is 2.6.32, I think; it certainly doesn't compile with
>> 2.6.38).
>>
>> So, while both of these may actually be good at what they do, neither of
>> them does what I have in mind and I also can't use either of them because I
>> need a newer kernel than what they support.
>>
>> But thanks anyway.
>>
>> --
>>                     Andras Korn <korn at elan.rulez.org>
>>                 I'm not nearly as think as you confused I am.
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>
>
>
> --
> Roberto Spadim
> Spadim Technology / SPAEmpresarial



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Roberto Spadim
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