[gpfsug-discuss] Wrong behavior of mmperfmon

[Dorigo Alvise (PSI)]

Hello,
I'm using mmperfmon to get writing stats on NSD during a write activity on a GPFS filesystem (Lenovo system with dss-g-2.0a).

I use this command:

# mmperfmon query 'sf-dssio-1.psi.ch|GPFSNSDFS|RAW|gpfs_nsdfs_bytes_written' --number-buckets 48 -b 1

to get the stats. What it returns is a list of valid values followed by a longer list of 'null' as shown below:

Legend:
 1:    sf-dssio-1.psi.ch|GPFSNSDFS|RAW|gpfs_nsdfs_bytes_written

Row           Timestamp gpfs_nsdfs_bytes_written
  1 2018-11-15-16:15:57                746586112
  2 2018-11-15-16:15:58                704643072
  3 2018-11-15-16:15:59                805306368
  4 2018-11-15-16:16:00                754974720
  5 2018-11-15-16:16:01                754974720
  6 2018-11-15-16:16:02                763363328
  7 2018-11-15-16:16:03                746586112
  8 2018-11-15-16:16:04                746848256
  9 2018-11-15-16:16:05                780140544
 10 2018-11-15-16:16:06                679923712
 11 2018-11-15-16:16:07                746618880
 12 2018-11-15-16:16:08                780140544
 13 2018-11-15-16:16:09                746586112
 14 2018-11-15-16:16:10                763363328
 15 2018-11-15-16:16:11                780173312
 16 2018-11-15-16:16:12                721420288
 17 2018-11-15-16:16:13                796917760
 18 2018-11-15-16:16:14                763363328
 19 2018-11-15-16:16:15                738197504
 20 2018-11-15-16:16:16                738197504
 21 2018-11-15-16:16:17                     null
 22 2018-11-15-16:16:18                     null
 23 2018-11-15-16:16:19                     null
 24 2018-11-15-16:16:20                     null
 25 2018-11-15-16:16:21                     null
 26 2018-11-15-16:16:22                     null
 27 2018-11-15-16:16:23                     null
 28 2018-11-15-16:16:24                     null
 29 2018-11-15-16:16:25                     null
 30 2018-11-15-16:16:26                     null
 31 2018-11-15-16:16:27                     null
 32 2018-11-15-16:16:28                     null
 33 2018-11-15-16:16:29                     null
 34 2018-11-15-16:16:30                     null
 35 2018-11-15-16:16:31                     null
 36 2018-11-15-16:16:32                     null
 37 2018-11-15-16:16:33                     null
 38 2018-11-15-16:16:34                     null
 39 2018-11-15-16:16:35                     null
 40 2018-11-15-16:16:36                     null
 41 2018-11-15-16:16:37                     null
 42 2018-11-15-16:16:38                     null
 43 2018-11-15-16:16:39                     null
 44 2018-11-15-16:16:40                     null
 45 2018-11-15-16:16:41                     null
 46 2018-11-15-16:16:42                     null
 47 2018-11-15-16:16:43                     null
 48 2018-11-15-16:16:44                     null

If I run again and again I still get the same pattern: valid data (even 0 in case of not write activity) followed by more null data.

Is that normal ? If not, is there a way to get only non-null data by fine-tuning pmcollector's configuration file ?
The corresponding ZiMon sensor (GPFSNSDFS) have period=1.
The ZiMon version is 4.2.3-7.

Thanks,

   Alvise

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