make immediate purge non-blocking up to 100,000 entries per drive

[harshavardhana]

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Description

make immediate purge non-blocking up to 100,000 entries per drive

Motivation and Context

non-blocking behavior for prefix deletes.

Bonus: Turn off O_DIRECT verification when FSType is 'XFS'

How to test this PR?

As the implementation behaves already

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Optimization (provides speedup with no functional changes)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• Fixes a regression (If yes, please add commit-id or PR # here)
• Unit tests added/updated
• Internal documentation updated
• Create a documentation update request here

[kannappanr]

LGTM