Re: Desynchronizing dm-raid1

["Martin K. Petersen" <mkp@mkp.net>]

>>>>> "Malahal" == malahal  <malahal@us.ibm.com> writes:

[I sent this last week but it never made it to the list]

Malahal> Very few drivers require it, so how about an interface to
Malahal> lock the pages of an I/O available to drivers. Only needed
Malahal> RAID drivers would lock the I/O while it is in progress and
Malahal> they only pay the performance penalty.  mmap pages are a bit
Malahal> tricky. They need to go into read-only mode when an I/O is in
Malahal> progress. I know this would likely be rejected too!!!

I have exactly the same problem with the data integrity stuff I'm
working on.

Essentially a checksum gets generated when a bio is submitted, and
both the I/O controller and the disk drive verify the checksum.

With ext2 in particular I often experience that the page (usually
containing directory metadata) has been modified before the controller
does the DMA.  And the I/O will then be rejected by the controller or
drive because the checksum doesn't match the data.

So this problem is not specific to DM/MD...

-- 
Martin K. Petersen	Oracle Linux Engineering