Lustre discuss - Apr 2010 - llapi stripe_size

calling llapi_file_create reports the following error:

error: bad stripe_size 4096, must be an even multiple of 65536 bytes: 
Invalid argument (22)

The operation manual said: This value must be an even multiple of system 
page size, as shown by getpagesize. The value 4096 above was returned 
from a call to getpagesize. (I don''t intend to set the stripe size so 
small, this is just to illustrate).

Where does the number 65536 come from, what''s the right way to
determine
it at runtime?

Thanks
Burlen

On 2010-04-16, at 11:07, burlen wrote:
> calling llapi_file_create reports the following error:
>
> error: bad stripe_size 4096, must be an even multiple of 65536 bytes:
> Invalid argument (22)
>
> The operation manual said: This value must be an even multiple of  
> system
> page size, as shown by getpagesize. The value 4096 above was returned
> from a call to getpagesize. (I don''t intend to set the stripe size
so
> small, this is just to illustrate).
>
> Where does the number 65536 come from, what''s the right way to  
> determine
> it at runtime?

The manual is incorrect in this case.  The correct limit is 65536  
bytes, not 4096.  It _used_ to be 4096 bytes, but since Linux supports  
client PAGE_SIZE up to 65536 bytes, and the VM cannot partially dirty  
a page, we do not support a stripe size that is smaller than a single  
page.

Cheers, Andreas
--
Andreas Dilger
Principal Engineer, Lustre Group
Oracle Corporation Canada Inc.