Data recovery from Linux server in this session considers the UBUNTU server with FTP clients. Topics discussed include file system recovery, partition fixing, restoration of application files and database restoration. Types of disk failure in the Linux environment and possible preventive care methods are also listed out. You need to read through the procedures to understand the algorithms involved in the recovery process. In most of the logical failures, software restoration will work effectively since many apps provide compatibility to Linux file systems and boot records & partitions. When the Linux disk drive in the server experiences physical breakdown, you will certainly need the help of hardware tools and OEM software applications to set right the issues. In both cases, the most recommended way is to take the help of professional data recovery expert for solving the basic issues of disk accessibility and getting data restored in secure manner.
Our system of data recovery solutions to UBUNTU server includes hardware scanning and testing equipments, software diagnosis and resetting applications. Our expert team will be able to solve any type of client server issues related to FTP workstations and dedicated server.
Basic scanning tools
Basic scanning tools can be obtained with the help of open source software which can be installed into the Linux server from the shell prompt. Invoking shell command for running one such application from DDRESCUE is “ddrescue <option> in-file out-files <optional-map-file>” from the shell prompt. In this command, ddrescue is the keyword for invoking the software application. In-file and out-file could be file names, device names or partition names.
Options with the command have multiple features depending on the nature and intensity of rescue and recovery operations. Here you get to read the most basic among them with a brief explanation about the purpose.
-A is an option for retrying the command for a specific period of time. When a scan and restore operation is run on a piece of data block which is not responding due to bad sectors or other physical issues. The ddrescue command is attempted by marking all the efforts to restore the data when the disk stops responding to the first time execution of the command. It will mark all the non-trimmed (failed in first attempt) and non-scrapped-data-blocks (ignored in the first attempt but not discarded as bad sector) as fresh blocks to be tried for data rescue operation.
–d is an option for using the method of accessing the disk directly for in-file. When this option is used, the UBUNTU kernel cache is ignored by ddrescue and the files in the failed tracks are recovered with O_DIRECT type of flag-setting. You need to specify the size of sector accurately for the successful execution of this option.
–D is an option for using the method of accessing the disk directly for out-file. When this option is used, the UBUNTU kernel cache is ignored by ddrescue and the files in the failed tracks are recovered with O_DIRECT type of flag-setting. You need to specify the size of sector accurately for the successful execution of this option.
If there is an error in specifying the sector size, files will not be recovered and the UBUNTU OS will display an error message in execution of the command.
–n is an option for avoiding the scrap-stage of the scan and rescue operation. That means ddrescue will ignore the sectors that have suffered critical damages from which the system is unable to read data.
–T <time-interval in seconds> (Example -T 50) is an option with time specifications for the number of retrials to read data from a failed block of data before stopping further attempts.
Benefits of ddrescue
Efficient rescue: – Once the rescue operation is initiated with proper set of parameters, the user does not need to interfere between the process stages for any reason. All the retries, skips, bug handling and other issues are managed by the system independently.
No overwriting: – ddrescue works on file rescue in many stages. That means a single target file can be written n-number of times by bringing in bits of information from the failed sectors. But it avoids the writing of zero to the target file when the source file sectors are found to be bad, that means it tries to append data to the existing target file rather than overwriting the target file each time. This approach helps in saving time during file recovery.
Disk support: – ddrescue extends support to all types of disk formats inclusive of ATA, SCSI, SD and SSD etc).
Rescue Algorithm: – The system works on 6 stages of recursive algorithm to produce effective data rescue operation. In the firsts stage it reads all the sectors with the help of a map-file (results from the previous rescue operations which are stored in the form of a log file). In case this is the first attempt to rescue the disk the system will create a new map file and writes the logs into it for further use in future.
In the next two stages, the system reads data from each sector only once and bypasses the bad sectors and non readable data. Once the first cycle of reading and writing is complete, the system attempts to read the data recursively, trying to append bits of data into the existing output files without overwriting them.
The system has the ability to read in both directions (forward and reverse); making sure that each block of data is read twice before moving onto the next blocks. Repeated attempts are made to read data from the bad sectors after marking all of them in one cycle of reading.
Once the write operation is complete, the system writes the log into new map-file and saves it for further use. It is possible for you to write the output to an external media by specifying it in the command line parameters. Make sure that you are well versed with all the options of the command line to produce effective results from ddrescue.