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NetWare Hard Drive Data Recovery

About NetWare File Systems

Netware, developed by Novell, dominated the mid-range networking market during the late 1980s and into the mid-1990s when its position was steadily eroded by Microsoft with its Windows NT product and successors, and then the rise of Linux which has gained popularity as a server operating system throughout the current decade. NetWare has since been replaced by OES (Open Enterprise Server).

NetWare gave shared access to NetWare volumes and other services such as printers as if they were attached to the local system that was logged into the NetWare server. The NetWare file system used from NetWare 3.0 (NWFS) was FAT based as with the MSDOS file system, but with enhancements to allow support for file names from systems that exceeded the 8.3 DOS convention. It was also possible to span file systems over multiple disks up to a 1TB limit, although NWS has a FAT32-like 4GB file size limit for individual files. NetWare 4 introduced enhancements such as the NDS and support for data compression within the file system, whilst remaining with the FAT format. Only with the release of NetWare 5 was a new file system, NSS, introduced although the SYS volume still had to use NWFS. NSS is a more UNIX/Windows style file system breaking away from the use of File Allocation Tables and having a node based organisation of files based around balanced tree.

NetWare NWFS Hard Drive Data Recovery

To begin with the problems that can cause a problem with any FAT based file system can have a dramatic impact upon the NetWare file system. Loss of FAT information removes any ability to locate the contents of files other than by identifying the contents, which can work with data such as Exchange EDBs but is not practical with most non-page based data formats. The second copy of FAT information does give a degree of protection, but any file deletion operation will eradicate both copies for the file in question and a system or hardware failure that causes data to be erroneously written will probably damage both FATs. With NetWare 4 the introduction of data compression is a double edged sword from the perspective of data recovery. A compressed file will not be readily identified by its contents, but it is more straightforward to determine that a file has been recovered correctly as the decompression will fail it it has not.

To work around the limiting factor of a file system with a large allocation unit size, that is that the final allocated cluster of a file contains free space and when a system contains large numbers of file the free space being wasted can be huge, NetWare introduce sub-allocation. Sub allocation works by maintaining a number of data files that are used to hold the "tail" of each file based upon the remainder of the file that is left at the end, the modulus of the file size and the cluster size. So for each file where the remainder is 512 bytes of less, the last block is put into the sub-allocation file for leftover bit that are 512 bytes of less. The same is then done for the powers of 2, 1024, 2048 and so forth. If sub-allocation is enabled then the amount of wasted space, or slack space, is minimised.

Data Recovery from a NetWare file system then there is limited damage FAT or some data loss causing faults within the directory structure usually results in a pretty high degree of success. Where FAT information is lost and sub-allocation is enabled the results are not usually so successful.

NetWare NSS hard drive data recovery

With NSS we gained the ability to salvage the data from the file system. It is practicable to use software to locate each leaf node within the file system and thence to rebuild the structures required to recover the data. The extent of the recovery will depend upon whether any leaf nodes are lost and whether there has been any re-use of file space, though with simple corruptions that prevent the file system from mounting a full recovery is usually achievable.

Last Updated (Tuesday, 09 June 2009 16:03)

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