When compiling Ceph, ccache may appear to miss more than expected, as shown by the cache miss line of ccache -s
cache directory /home/loic/.ccache cache hit (direct) 1 cache hit (preprocessed) 0 cache miss 1 files in cache 3 cache size 392 Kbytes max cache size 10.0 Gbytes
Compiling Ceph from clones in two different directories does not explain the miss, unless CCACHE_HASHDIR is set. It should be unset with:
unset CCACHE_HASHDIR