[Linux-cluster] Unformatting a GFS cluster disk

[Lombard, David N]

On Fri, Mar 28, 2008 at 04:54:22PM -0500, Wendy Cheng wrote:
> christopher barry wrote:
> >On Fri, 2008-03-28 at 07:42 -0700, Lombard, David N wrote:
> >  
> >>On Thu, Mar 27, 2008 at 03:26:55PM -0400, christopher barry wrote:
> >>    
> >>>On Wed, 2008-03-26 at 13:58 -0700, Lombard, David N wrote:
> >>>>A fun feature is that the multiple snapshots of a file have the 
> >>>>identical
> >>>>inode value
> 
> Wait ! First, the "multiple snapshots sharing one inode" 
> interpretation about WAFL is not correct.

Same inode value.  I've experienced this multiple times, and, as
I noted, is a consequence of copy-on-write.

I've also had to help other people understand why various utilities
didn't work as expected, like gnu diff, which immediately reported
identical files as soon as it saw the identical values for st_dev
and st_ino in the two files it was asked to compare.

>From the current diffutils (2.8.1) source:

  /* Do struct stat *S, *T describe the same file?  Answer -1 if unknown.  */
  #ifndef same_file
  # define same_file(s, t) \
      ((((s)->st_ino == (t)->st_ino) && ((s)->st_dev == (t)->st_dev)) \
       || same_special_file (s, t))
  #endif

>                                            Second, there are plenty 
> documents talking about how to do snapshots with Linux filesystems 
> (e.g. ext3) on Netapp NOW web site where its customers can get 
> accesses.

I didn't say snapshots don't work on Linux.  I've used NetApp on
Linux and directly benefitted from snapshots.

-- 
David N. Lombard, Intel, Irvine, CA
I do not speak for Intel Corporation; all comments are strictly my own.