[TOPIC LPC] Filesystem Shrink

[Allison Henderson <allison.henderson@oracle.com>]

Hi All,

Earlier this month I had sent out a lpc micro conference proposal for
file system shrink.  It sounds like the talk is of interest, but folks
recommended I forward the discussion to fsdevel for more feed back.
Below is the abstract for the talk:


File system shrink allows a file system to be reduced in size by some 
specified size blocks as long as the file system has enough unallocated 
space to do so.  This operation is currently unsupported in xfs.  Though 
a file system can be backed up and recreated in smaller sizes, this is 
not functionally the same as an in place resize.  Implementing this 
feature is costly in terms of developer time and resources, so it is 
important to consider the motivations to implement this feature.  This 
talk would aim to discuss any user stories for this feature.  What are 
the possible cases for a user needing to shrink the file system after 
creation, and by how much?  Can these requirements be satisfied with a 
simpler mkfs option to backup an existing file system into a new but 
smaller filesystem?  In the cases of creating a rootfs, will a protofile 
suffice?  If the shrink feature is needed, we should further discuss the 
APIs that users would need.

Beyond the user stories, it is also worth discussing implementation 
challenges.  Reflink and parent pointers can assist in facilitating 
shrink operations, but is it reasonable to make them requirements for 
shrink?  Gathering feedback and addressing these challenges will help 
guide future development efforts for this feature.


Comments and feedback are appreciated!
Thanks!

Allison