In the current version, you cannot change the cluster size once a file has been compressed. You must decompress the file first, and make sure no process has the file still open before compressing it again with the new cluster size.
In the current version, if you change the compression algorithm for a compressed file, already-compressed clusters will not be recompressed with the new algorithm. If you want to do so, you should decompress the file first, and make sure no process has the file still opened before compressing it again with the new algorithm. An exception is made for the `none' algorithm: changing from `none' to some other algorithm results in the kernel attempting to compress all currently-uncompressed clusters. (Clusters already compressed with some other algorithm are left compressed in that algorithm.)
Historical information: In the versions 0.1a and 0.1b, only the first 16
clusters would be compressed. The other ones would remain uncompressed.
The reason is that it would require to patch e2fsck in order to
store a bigger bitmap for compressed clusters (currently, e2fsck
would reclaim the block where we would store the bitmap, because it
would fail to see that it is used). This limitation does not hold
anymore in version 0.1c and later, provided you patched e2fsck
and installed the new e2fsck.
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