melman@techunix.BITNET (David Melman) (07/04/89)
I have been request to help a desperate doctorial student who has lost an entire year's worth of work on his Silicon Graphics (Iris) workstation system version 2.0. Out of ignorance, NO BACKUPS were done! The machine was taken down immediately afterwards, so hopefully the freed data blocks have not been overwritten. Initially, I thought I was dealing with a conventional SysVR3 file system. I looked up in Bach's "The Design of the Unix Operating System" and discovered that when the inode link count reaches zero, the inode is left intact except for the file type (di_mode) field, which gets zeroed out. So, I thought all I need to do is run through the i_list looking for his UID, and mark the file type. I was going to determine the file type (either regular file or directory) by looking at the first data block. Then fsck would find all the orphaned files and pop them in lost+found. Then I discovered that their file system is something called the "Extent File System" which I have never heard of. The structure uses cylinder groups so I guess it has some Berkeley file system aspects (?). Does it also just zero the file type field in the inode when freeing it? Can anybody give me information about this file system to enable me to restore these files? David Melman BITNET: melman@techunix.bitnet Internet: melman%techunix.bitnet@cunyvm.cuny.edu