Re: [netcdfgroup] netCDF4 file bit-for-bit reproducibility?

• To: zender@xxxxxxx, ymuqun@xxxxxxxxxxxx, epourmal@xxxxxxxxxxxxx, slu@xxxxxxxxxxxx, koziol@xxxxxxxxxxxx
• Subject: Re: [netcdfgroup] netCDF4 file bit-for-bit reproducibility?
• From: Ed Hartnett <ed@xxxxxxxxxxxxxxxx>
• Date: Tue, 08 Jan 2008 08:39:56 -0700

Charlie Zender <zender@xxxxxxx> writes:

> Hi and happy new year to the netCDF group,
>
> Will netCDF4 make bit-for-bit (BFB) reproducible files?
> In other words will running a determinstic model twice on the same
> machine (without changing compiler, netCDF library, etc.) produce
> identical output files?
> I thought that netCDF4 would, like netCDF3, use deterministic
> algorithms without any date-stamps within the file, and thus produce
> BFB files. Apparently I am wrong.
>
> To determine whether files were BFB I checked their SHA1 sums.
> netCDF3 produces BFB files and netCDF4 (snapshot) does not (below).
> BFB output files make models easier to debug, so it would be helpful
> if netCDF4 continued the netCDF3 BFB "tradition". Is this possible?
> Am I missing something? Is HDF5 the culprit?
>
> Thanks,
> Charlie
>

Howdy Charlie!

I is my understanding that HDF5 does not guarantee the bit-or-bit
reproducibility of their files. I have forwarded this to them to
confirm this...

I'm afraid there is nothing I can do at the netCDF-4 level to change
that.

Thanks,

Ed
-- 
Ed Hartnett  -- ed@xxxxxxxxxxxxxxxx

• Follow-Ups:
  • Re: [netcdfgroup] netCDF4 file bit-for-bit reproducibility?
    • From: Charlie Zender
  • Re: [netcdfgroup] netCDF4 file bit-for-bit reproducibility?
    • From: Quincey Koziol

• References:
  • [netcdfgroup] netCDF4 file bit-for-bit reproducibility?
    • From: Charlie Zender