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

David George david at thegeorges.us
Wed Jan 2 15:43:11 UTC 2008

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.


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