Did anyone know what it means? (It used in ScheduledDefrag task)

That's odd. My defrag.exe command in Task Scheduler is %windir%\system32\defrag.exe -c -i, which means the -i is not documented (but -c tells me I'm defragmenting all attached volumes):

Microsoft Windows [Version 6.0.6001]
Copyright (c) 2006 Microsoft Corporation.  All rights reserved.

C:\Users\thisuser>defrag /?
Description:  Locates and consolidates fragmented files on local volumes to
			  improve system performance.

Syntax:  defrag <volume> -a [-v]
		 defrag <volume> [{-r | -w}] [-f] [-v]
		 defrag	   -c [{-r | -w}] [-f] [-v]

Parameters:

Value		 Description

<volume>	  Specifies the drive letter or mount point path of the volume to
			  be defragmented or analyzed.

-c			Defragments all volumes on this computer.

-a			Performs fragmentation analysis only.

-r			Performs partial defragmentation (default). Attempts to
			  consolidate only fragments smaller than 64 megabytes (MB).

-w			Performs full defragmentation. Attempts to consolidate all file
			  fragments, regardless of their size.

-f			Forces defragmentation of the volume when free space is low.

-v			Specifies verbose mode. The defragmentation and analysis output
			  is more detailed.

-?			Displays this help information.

Examples:

defrag d:
defrag d:\vol\mountpoint -w -f
defrag d: -a -v
defrag -c -v

I did some searching and found that -i tells defrag.exe to pause when the machine is not idle (hence -i).

I read somewhere that -i switch means "work only if system is idle for few minutes", it's not documented because was added after freeze of language packs (still I don't understand why not update language packs, even if they can't do that before release they can do it with windows update)

BTW, my system is Vista x64 SP1.

I found that Defrag.exe /G does optimization in a tiered layout, i.e., if you have a storage pool containg HDDs and SSDs, it will do a special defragmentation: Frequently accessed data will be stored on the SSDs and the remaining will be on the HDDs.

Check more at What's New in Defrag for Windows Server 2012/2012R2 and at Storage Spaces: How to configure Storage Tiers with Windows Server 2012 R2.

Edited December 19, 20169 yr by joaopaulo1511