Re: support for external persistent cache

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

if /dev/sdb get full, /dev/sda must be sync before continue...
it´s a background thread
but it works like linux memory cache, but linux use ram (volatille)
you want a volatille (ssd)

it´s like this:
http://www.seagate.com/www/en-us/products/laptops/laptop-hdd

2011/1/19 Roberto Spadim <roberto@spadim.com.br>:
> yes, a jornaling but using ssd first and sata after
> it´s not raid feature...
> it´s per disk filesystem feature...
> we could implement jornaling in raid too...
> but´s more inteligent (easy) at application level (filesystem)
> you could write first at network (if it´s faster than sata) and after
> at sata (if it´s slower than network)
>
> it´s not a raid feature... it´s a per device feature got it?
> maybe a device (not raid..) for a cache division on devices
> for example
>
>
> /dev/sda (sata 1terabyte 100mb/s)
> /dev/sdb (ssd 1gigabyte 1000mb/s)
>
> /dev/cache_a (a mix of sata and ssd with sata size 1terabyte, and
> mixed speed (memory, ssd, sata))
>
> cache_a device should know that
> early reads/write should be writen to sdb
> time in time it should sync at sda
>
> the same happens with memory (ram memory) but it´s volatille (diferent
> than ssd that´s not volatille)
>
> /dev/sdb should be sync
> /dev/sda should be async (since /dev/sdb make it safe to use async)
>
>
> that´s you intention? i don´t know if linux have it, anyone know?
>
>
> 2011/1/19 Cory Coager <ccoager@gmail.com>:
>> On Wed, Jan 19, 2011 at 02:16:08PM -0200, Roberto Spadim wrote:
>>> ok, your hardware have:
>>> cpu, memory, disk controller, disks
>>>
>>> and you computer have:
>>> cpu, memory, disk controler (your hardware)
>>>
>>> if your computer cache don?t sync to your disk controller you will
>>> lose information....
>>>
>>> check that *memory, is the volatille memory and *disk controller is
>>> the non volatille memory
>>> if you tell me that you will never have a *memory, and you have always
>>> a non volatille memory, no problem, you will never need a kernel
>>> load... just a boot loader that read previous memory information and
>>> start in that point... why don?t do this? non volatille memory is not
>>> as fast as volatille memory
>>> got the problem?
>>
>> Sorry, we're still not on the same page.  I would use both a ramdisk
>> and sata disk.  The ramdisk would act as a persistent cache
>> (with the battery) for the sata disks.  Enabling write through
>> would write to the cache first then sync to the sata disks.
>>
>> Understand what I'm getting at now?
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>
>
>
> --
> Roberto Spadim
> Spadim Technology / SPAEmpresarial
>



-- 
Roberto Spadim
Spadim Technology / SPAEmpresarial
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