Novell Operating System - Recovery of Sub-Allocated Volumes

Problem Description

Data storage in Novell servers is optimized using sub-allocated volumes. Sub-allocated volumes are a new feature and have been implemented on Netware 4.x to overcome the problem of wasted disk space. These volumes are different from regular Novell volumes because they are more of a virtual volume one that is not visible, but exists nevertheless - and this is what complicates the issue. Since they are not physically visible, a separate data recovery module has to be incorporated into the software to ensure complete recovery.

Technical Aspect of the Problem

Sub-allocation refers to multiple file-endings sharing disk blocks. The data in a file is stored in the hard disk in multiple blocks, each block being a collection of sectors of standard size. There are, almost always, some unutilized sectors at the end of a file. These under-allocated sectors of different files are combined together to form a separate virtual volume.

For Example: Say, a volume stores data in blocks of 4 sectors, each sector having size = 512 bytes. A block is the minimum amount of space that can be assigned to a file. Now, if there is a file containing 520 bytes of data, the first sector is entirely occupied and the remaining 8 bytes go into the second sector. This leaves 2 entire sectors unused. These unutilized sectors of different files are combined together to form a separate sub-allocated volume, thus saving space and optimizing data storage.

The sub-allocated volume is virtual, that is, it does not show up as a separate logical volume. It is internally used by the Operating System (Netware 4.x) to optimize disk space utilization, and data recovery from such volumes thus needs advanced software.

Technical Aspect of the Solution

Phoenix Novell is a Windows based application and can only be installed on a Windows based hard disk. Therefore, the failed Novell based disk needs to be attached as a secondary disk to a Windows based disk with Phoenix installed in it. After the damaged disk is attached, Phoenix needs to be run from the working disk.

The software first detects all the disks along with the associated volumes/partitions and displays the list. It then scans the selected volume and displays the list of found data. While scanning the visible volume, the software also uses an advanced module to detect and scan the invisible sub allocated volume. After the scan is complete, all the details are listed in a simple tree structure and any number of files can be selected for recovery.

Working of Phoenix Novell

The damaged server disk needs to be connected as a secondary to a working Windows based disk with Phoenix Novell installed in it. The software is then run to start the recovery process.

Clicking Select Netware Partition will display a list of hard disks with their respective volumes. Select the damaged volume on the server disk to start the scan process. Apart from scanning the selected volume, a separate software module also detects and scans the virtual sub allocated volume. The entire list of found data (from the regular Netware volume and its sub allocated volume) is then displayed.

Any number of files can be selected for recovery, and clicking Recover Selected will restore the selected files. Alternatively, clicking Recover Deleted will recover all the files listed in the displayed list of files.

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