GeorgeVandenberghe-NOAA
commented
11 months ago The Grib1 library was originally developed on IBM MVS systems in the 1980s and early 90s and the "file" on disk was a much more complex object with blocking and record sizes maintained in their analog to an inode which was an entry in the disk catalog describing the file. Grib1 files had to be streams of bits (like Unix files) with all of those descriptor entries empty. This was IBM MVS file type unblocked or u. All of this IBM MVS "crap" did improve disk performance by laying files fairly efficiently on disk and reducing fragmentation a lot.
The concept of blocked at the file level is irrelevant on unix systems for unix system calls. Blocking is critical in the filesystem code but programmer mistakes there cause performance problems, not errors (generally fatal in MVS) returned to the program.
On Sun, Sep 10, 2023 at 4:38 AM Edward Hartnett @.***> wrote:
In the utility grbindex.f we say:
!> The index file serves as a table of contents for the GRIB1 file, !> enabling quick access to the data. The GRIB1 file must be unblocked, !> but there can be a gap before the first grib message of at most 32000 !> bytes and gaps between messages of at most 4000 bytes.
What does unblocked mean?
In fortran we can have formatted vs. unformatted files, is that what is meant here?
@GeorgeGayno-NOAA https://github.com/GeorgeGayno-NOAA @GeorgeVandenberghe-NOAA https://github.com/GeorgeVandenberghe-NOAA @AlexanderRichert-NOAA https://github.com/AlexanderRichert-NOAA @Hang-Lei-NOAA https://github.com/Hang-Lei-NOAA any gueses?
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George W Vandenberghe
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edwardhartnett
In the utility grbindex.f we say:
!> The index file serves as a table of contents for the GRIB1 file, !> enabling quick access to the data. The GRIB1 file must be unblocked, !> but there can be a gap before the first grib message of at most 32000 !> bytes and gaps between messages of at most 4000 bytes.
What does unblocked mean?
In fortran we can have formatted vs. unformatted files, is that what is meant here?
@GeorgeGayno-NOAA @GeorgeVandenberghe-NOAA @AlexanderRichert-NOAA @Hang-Lei-NOAA any gueses?