PowerScale : OneFS : Isilon : How to switch between the Scan Mode and IndexUpdate modes of the FSAnalyze Job

In OneFS 8.2 and later versions FSAnalyze job cab run in two modes:

Index Mode (New Default)

The Index mode relies on Index snapshots and change lists, updates, and walks a global metadata index.
This is enabled by the following gconfig value setting:
 

isi_gconfig -t job-config jobs.fsa.snap_based_mode=true

Please note that above is the default value for this sysctl.
In this mode phase-7 index_walk is utilized.


Scan Mode (Old style)

The scan mode scans the OneFS file system entirely.
This can be enabled by the following gconfig value setting:
 

isi_gconfig -t job-config jobs.fsa.snap_based_mode=false

In this mode phase-8 lin_fsa (a.k.a lin_walk) is utilized in place of phase-7.

The (old style) Scan mode also supports (old style) FSAnalyze snapshots. (a.k.a. FSA snapshots)
To turn on FSA snapshot:
 

isi_gconfig fsa.use_snapshot=true

Index Mode does not get any benefit from FSA snapshot:

The Index (default) mode of FSA runs faster if an IndexUpdate job is ran before the FSAnalyze job.
The old style FSA snapshots (isi_gconfig fsa.use_snapshot=true) does not have any positive affect in FSA performance in Index mode as well as scan mode, although it creates FSA snapshots.