[mythtv-users] Compact Flash write cycles (was: Re: Intro---)

[David George]

On 01/01/2008 05:48 AM, Stroller wrote:
> On 1 Jan 2008, at 06:20, Mike Barnard wrote:
>   
>>> Since I'll probably have MySQL running on
>>> the system disk (CF) I wondered if the 4GB CF would be sufficient  
>>> space
>>> for all that file handling. Or should I just nix it for a HDD.
>>>       
>>     I was actually considering the same thing. I have some IDE-to-CF
>> adapters, and I like the idea of low power consumption and complete  
>> lack
>> of noise. However, there's just no way CF would hold up for any length
>> of time given the level of write activity involved in Myth (especially
>> with MySQL).
>>     
>
> This is something I'm interested in, but haven't tried. I understood  
> that modern flash devices would handle many more writes than early ones.
>   

This is true.  Early flash was 100,000 writes.  Current NAND flash is 
typically 1,000,000 writes.  However this is writes to a sector 
(smallest writable unit).  The other catch is you will really want to 
use a filesystem designed specifically for wear-leveling like YAFFS.  
With 1,000,000 writes, if you write to the same sector once per second, 
you get about twelve days worth of writes.
> A quick Google:
>
>    ... some industry analysts[2] have calculated that flash memory  
> can be
>    written to at full speed continuously for 51 years before exceeding
>    its write endurance, even if such writes frequently cause the entire
>    memory to be overwritten. This figure (51 years) involved a worst- 
> case
>    scenario using specific data parameters and should not be confused
>    with a particular "shelf life" for a flash memory device.
>    [from <http://en.wikipedia.org/wiki/Flash_memory#Limitations>]
>   

I am not sure that compact flash devices have the built-in wear leveling 
mentioned in the article.  SD may.  I haven't researched that far into 
it as we usually work with NAND flash using YAFFS in the embedded 
systems at work.

-- 
David