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9-2 Dell PowerVault 720N, 740N, and 760N System Administrator and Command Reference Guide
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Snapshot files carry the same permissions and inode numbers as the original files,
keeping the integrity of the security system intact. Inodes are data structures that
hold information about files on the filer. There is an inode for each file and a file is
uniquely identified by the file system on which it resides and its inode number on that
system.
NOTE: The inode number for a file in a snapshot is the same as the inode number for
the corresponding file in the active file system. As a result, some programs on UNIX
clients consider the two files to be the same. For example, if you use the GNU
diff
program to compare the two files, it does not find any differences between them. To
make sure that the two files have different inode numbers before the comparison,
copy one of the files to another name.
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When the filer creates a snapshot, it doesnt copy disk blocks; instead, it identifies all
blocks in the file system as belonging to the snapshot as well as to the active file
system.
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Consider a particular file named foo in a newly created snapshot. Because the snap-
shot was just created, the snapshot version of foo has the same contents as the
version in the active file system. The same blocks on disk store both versions, so the
snapshot version of foo consumes no disk space.
Later, if foo is deleted, the blocks holding the data for foo are no longer part of the
active file system, but they are still part of the snapshot. Therefore, deleting
foo from
the active file system does not free any disk space.
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Figure 9-1 illustrates how disk space is used before and after foo is removed.