Re: Converting system to raid

[Jeff Garzik <jeff@garzik.org>]

jim owens wrote:
> Jeff Garzik wrote:
>> jim owens wrote:
>>> nanosecond time stamps are a myth!
>>
>> Not true, in the age of NO_HZ...
> 
> While nanosecond time is real on some hardware platforms,
> I don't know of any hard disk filesystem that does metadata
> updates at that level of granularity and guarantees distinct
> timestamps between writes at extremely short intervals.
> 
> Even SSD performance would suck if we did that.
> 
> The filesystem mod-time might have nanoseconds in it, but
> that does not mean 2 writes 100 nanoseconds apart will have
> different mod-times.

Modern Linux filesystems absolutely do do metadata updates at that level 
of granularity.

Are you guaranteed district timestamps between writes?  No, but then 
again, metadata updates were never guaranteed between two writes either. 
  You might just be dirtying a mmap'd page, for example.

	Jeff