[Ocfs2-users] Understanding debugfs.ocfs2 output

[Sunil Mushran]

The length of allocator chains in the global bitmap depends on
the size of the volume and block/cluster sizes. It is created during
format and only grows if the volume is grown. That's it.

On 11/23/2010 11:04 AM, Norman P. B. Joseph wrote:
> This is related to the "No space on OCFS2 volume" error discussed here
> this past Sep/Oct.  Our Oracle support rep pointed us to Metalink note
> #1232702.1 and suggested we should script something up to periodically
> check the free contiguous blocks in the group chains for the volume in
> question.
>
> Reading the note, I get how to get Clusters per Group X Bits per Cluster
> from the "stat //extent_alloc:NNNN".  What I'm confused about is parsing
> the "stat //global_bitmap" section, and I thought I might have a better
> chance of getting an explanation from the audience here.
>
> I have 2 basic questions:
>
> 1) The note above says that a "highly fragmented volume will have many"
> Group Chain entries in the //global_bitmap section, but gives no
> guidance as to what constitutes "many".  I see ~240 in the 56 GB OCFS2
> partition in question.  Is that Low?  High?  Just Right?
>
> 2) The note also says to check the "Contig" values in the long list of
> Group Chains that follows in the //global_bitmap section.  Specifically,
> "If none are higher than the sum[sic] of "Clusters per Group * Bits per
> Cluster" the metadata extent file cannot be expanded..."  Here is a
> sample output below:
>
>          Group Chain: 8   Parent Inode: 11  Generation: 1861766630
>          CRC32: 00000000   ECC: 0000
>          ##   Block#            Total    Used     Free     Contig   Size
>          0    258048            32256    1026     31230    28159    4032
>          1    8096256           32256    1        32255    32255    4032
>
>          Group Chain: 9   Parent Inode: 11  Generation: 1861766630
>          CRC32: 00000000   ECC: 0000
>          ##   Block#            Total    Used     Free     Contig   Size
>          0    290304            32256    30721    1535     1535     4032
>          1    8128512           32256    1        32255    32255    4032
>
>          Group Chain: 10   Parent Inode: 11  Generation: 1861766630
>          CRC32: 00000000   ECC: 0000
>          ##   Block#            Total    Used     Free     Contig   Size
>          0    322560            32256    31745    511      511      4032
>          1    8160768           32256    1        32255    32255    4032
>
>          Group Chain: 11   Parent Inode: 11  Generation: 1861766630
>          CRC32: 00000000   ECC: 0000
>          ##   Block#            Total    Used     Free     Contig   Size
>          0    354816            32256    30721    1535     1535     4032
>          1    8193024           32256    1        32255    32255    4032
>
> Should I be considering -all- the Contig values from -all- the Group
> Chains listed when looking for issues, or should I be considering each
> chain individually?  IOW, is it only a problem when -all- the Contig
> values from -all- the chains are below the clusters X bits value, or is
> it only a problem when all of the Contig values for a -single- chain are
> below the cluster X bits value?
>
> Any pointers on valid interpretation of the output is appreciated.
>
> -Norm
>
>