[Ocfs2-users] Understanding debugfs.ocfs2 output

[Norman P. B. Joseph]

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


-- 
Norman Joseph, Senior System Engineer              joseph at ctc.com
Concurrent Technologies Corporation                 814.269.2633
Information Systems Management Office (ISMO)



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