Jon Craig wrote:
> 2009/8/31 Christian Völker <chrischan AT knebb DOT de>:
>> Yohoo!
>>> With backuppc the issue is not so much fragmentation within a file as
>>> the distance between the directory entry, the inode, and the file
>>> content.  When creating a new file, filesystems generally attempt to
>>> allocate these close to each other, but when you link an existing file
>>> into a new directory, that obviously can't be done so you end up with a
>>> lot of long seeks when you try to traverse directories picking up the
>>> inode info.
> 
> I believe you are mistaken in this.  Your confusing directory entries
> with inode entries. 

No, I'm saying that the filesystem has a choice about what inode and 
free space to use when the first entry is created.  And a sensible 
filesystem will try to cluster them or at least keep the inodes 
allocated for files created in the same directory close together.

> When you hard link a file from one directory to
> another you have two directory entries pointing to the same inode.

And the new directory entry may be all the way across the disk from the 
existing inode - and far from any other inode in this directory.

> You can do a simple test by touching a file and then make a hard link
> to a new file and list with "ls -li".  You will see that both files
> share the same inode number.

And, assuming you have enough disk activity to keep the cache out of 
date, that 'ls -l' will have to move the disk head to the directory 
location and then the inode to get the data - if you list many files in 
the same directory that were links to existing files, the head may have 
to seek all over the place to get the inoded data.

-- 
    Les Mikesell
     lesmikesell AT gmail DOT com


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