These days we have moving our glorious testbeds to new hardware, that has apparently a supercharged CPU and a poor disk system.
Initially the metadata performance was unacceptable, thus we have come out with an updated set of mysql tuning hints, that gave a boost of around 20 times to the stat and ls operations, which are very important indicators. Now the performance is very good, and the testbeds will enter production very soon.
The parameters are:
innodb_flush_log_at_trx_commit=2 innodb_flush_method=O_DIRECT innodb_buffer_pool_size=1GB innodb_doublewrite=0 innodb_support_xa=0 innodb_thread_concurrency=8 query_cache_limit=1M query_cache_size=256M
I have updated the tuning hints page with the new mysql parameters.