LINUX accidentally deleted the Oracle database, data recovery technology program

LINUX accidentally deleted the Oracle database, data recovery technology program
Preface:
     The Ext3/Ext4 under LINUX file system, if you accidentally deleted data, data recovery is
very difficult. Said to delete the file number of small (usually less than hundreds of files), but
also through the journal log files residues in contrast to the inode information recovery, restore
data directory structure may not be able to retain the integrity of; If you delete the file number
large, data recovery is almost intact the file directory structure. This is a common problem with
the Ext3/Ext4 the file system, not to the deletions go backward! In the case of the data recovery
industry, there are many examples of the ORACLE database file is accidentally deleted LINUX, I
Laijiang Jiang delete the Oracle database under Linux data recovery technology program.


Data loss case background:
     Computer maintenance engineers stopped the oracle services, oracle intend to do a cold
backup, backup the library file to the windows PC Server, download with CuteFTP customer side.
During the download process, the download speed is slow, want to delete the download tasks, the
results of misuse, you want to download oracle instance folder removed, the oracle library files,
control files, log files deleted in its entirety.

Under LINUX EXT3 file system recovery technologies introduced:
     EXT3 file system is not set aside the undelete function.
     EXT3 file system, each file are Inode describe the specific location of its data storage,
data pointer part of inode is cleared when files are deleted after the file directory area is not
much variation. File read and write through Inode, Inode data pointer is cleared, even if the
contents of the file still we have no way combination of the contents of the file.
     EXT3 file system is a file system with a log function, the inode changes in the log files
recorded in the journal in the journal file is relatively small, usually 32MB. EXT3 file system
metadata change, the corresponding metadata. The journal file will have a the COPY. For example, a
file is deleted, the Inode information. The journal file to keep a, and then you want to delete
the file inode information is cleared. This. The journal file is recycled, when the operation is
too much, the deleted file's inode logging new data substitution, which completely lost the
opportunity to retrieve data according to the inode. If a large number of files to delete. The
journal file has been repeatedly recycled many times, only to leave the last deleted file recovery
the opportunity to.

Data recovery technology:
     Customers to recover oracle database, oracle database files are deleted, as long as the data
is not covered, Darth data recovery files can be extracted separately.
After in-depth analysis not found. The journal file to delete the oracle data files, because the
user to delete the data, the system is still switched on at the same time try to start the oracle
instance, oracle to generate some log files, the number of these log files. the number of deleted
files to be restored only 16. journal file does not delete the file inode information.
To restore the idea of ??two:
First: According to the internal structure of the oracle data files on a comprehensive search, in
line with data from the oracle data pages are extracted, and then reassembled in accordance with
the ID number of the Oracle data files.
The second: Distribution Law according to the oracle data files, precise positioning of the oracle
file data pointer address, including an indirect address, two indirect address and three indirect
address, re-construct the file's inode information, and then read the data out.

Through these two recovery data are good, the last oracle to start normally. Engineers all the
data backup, the last two tables of data a little something to record, has been identified as the
reason for this is to delete the file after the log files written to the partition, and destroyed
some of the data page of the Oracle data files, but fortunately this two tables of data for users
is not very important.