When you run Check Disk, most often you see a message 'CHKDSK is deleting index entry in index $I30'. Here I'll summarize why this message is displayed during Check Disk repairing disk errors in Windows XP, 7, 8 etc. Besides, the post will give you an idea about index entry in $I30 file.
In NTFS file system, an index of all files & directories are stored in $I30 attribute. Every directory has its own $I30 attribute that maintain indices in B-tree structure. Moreover, when addition or deletion of files occur, $I30 attribute re-arrange its index records suitably. But it may leave slack space having remnants of the removed file.
There are several reasons why CHKDSK is deleting index entry in index $i30 from Windows, some of the reasons are elaborated here:
NTFS follows the procedure that it first stores information in a log file then writes data to a disk. CHKDSK only reads data structure on the disk, neither it reads log file nor cached RAM data. So, if for some reason data has not been copied to a disk then Check Disk starts deleting index entry as file record must not have been written yet.
Another reason for deleting index entry is when the file having security permission has been removed then it is sure that its ACL (Access control list) still exists. CHKDSK attempts to delete ACLs that cannot be used any longer.
It is presumed that "CHKDSK deleting index entry in $I30" deletes only index entry & it doesn't delete actual data since files had already been lost, corrupt or damaged. It seems impossible to restore damaged orcorrupt files as they cannot be seen by operating system any longer. Nevertheless, there is the simplest way to recover corrupt files. You can use windows file recovery software with a view to getting back all deleting index entry files.