Re: [PATCH][RFC] resize2fs and uninit_bg questions

[Andreas Dilger <adilger@sun.com>]

On Sep 18, 2009  07:43 -0400, Ric Wheeler wrote:
> On 09/18/2009 02:09 AM, Martin K. Petersen wrote:
>>>>>>> "Ric" == Ric Wheeler<rwheeler@redhat.com>  writes:
>>>>>>>              
>> Ric>  One note - the WRITE_SAME command in SCSI has long been used by
>> Ric>  array vendors to do relatively high performance zero fills.
>>
>> I've been working on WRITE SAME and UNMAP support recently (layering on
>> top of Christoph's patch kit).  It might be worthwhile to expose the
>> WRITE SAME functionality further up the stack.  It could also be helpful
>> for initializing RAID disks, for instance...
>
> Using it to initialize RAID disks is exactly what it is there for - that  
> sounds quite useful...

In ext4 we already have a routine ext4_ext_zeroout() that is used to zero
out chunks of disk in order to wipe uninitialized extents when they need
to be put into use.  It currently maps ZERO_PAGE() multiple times to avoid
causing cache pressure, but if we could wire it up to some block-level
routine that optimized this it would be even better.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.