Many people have been complaining about bad performance 
with lessfs. The problem is often that lessfs is mounted
with a 4k blocksize. When you mount lessfs with a 4k 
blocksize an enormous amount of metadata has to be 
stored. This reduces the performance in a really bad way.
Please use lessfs with a blocksize of at least 32k.
Using lessfs with a 64k or 128k blocksize is advised.
In most cases 128k gives the best result.

./lessfs /etc/lessfs.cfg /fuse  -o negative_timeout=0,\
  entry_timeout=0,attr_timeout=0,use_ino,readdir_ino,\
  default_permissions,allow_other,big_writes,\
  max_read=131072,max_write=131072 

When your system has multiple disks it makes sense to
store the meta data on different low latency disks (raid1)
or even better SSD.

BLOCKUSAGE_PATH and FILEBLOCK_PATH are the most important
candidates to store on separate disks when lessfs is 
used with tokyocabinet. If you are using BerkeleyDB or 
hamsterdb then point META_PATH to your low latency (SSD) drive.
