InfoScale™ 9.0 Storage and Availability Management for DB2 Databases - AIX, Linux

Storage Checkpoints and 64-bit inode numbers

The inode number of a file is the same across Storage Checkpoints. For example, if the file file1 exists in a file system and a Storage Checkpoint is taken of that file system, running the stat command on file1 in the original file system and in the Storage Checkpoint returns the same value in st_ino. The combination of st_ino and st_dev should uniquely identify every file in a system. This is usually not a problem because Storage Checkpoints get mounted separately, so st_dev is different. When accessing files in a Storage Checkpoint through the Storage Checkpoint visibility extension, st_dev is the same for all Storage Checkpoints as well as for the original file system. This means files can no longer be identified uniquely by st_ino and st_dev.

In general, uniquely identifying all files in a system is not necessary. However, there can be some applications that rely on unique identification to function properly. For example, a backup application might check if a file is hard-linked to another file by calling stat on both and checking if st_ino and st_dev are the same. If a backup application were told to back up two clones through the Storage Checkpoint visibility extension at the same time, the application can erroneously deduce that two files are the same even though the files contain different data.

By default, Storage Foundation (SF) does not make inode numbers unique. However, you can specify the uniqueino mount option to enable the use of unique 64-bit inode numbers. You cannot change this option during a remount.