Hi, our squid system (according to our munin graphs), is suffering rather from high iowait. I'm also seeing warnings of disk i/o overloading. I'm interested to understand how this disk load scales. I know more disks (we only have a single cache disk just now) would be a big help. One question I have is how (and if) the disk load scales with the size of the cache. I'll present a ludicrously simplistic description of how disk load might scale (purely as a starting point) and see could people point out where I'm wrong. The job a single disk running a cache must do in some time step might be: disk_work = (write_cached_data) + (cache_replacement_policy) + (read_hits) where: (write_cached_data) =~ x * (amount_downloaded) (cache_replacement_policy) = (remove_expired_data) + (LRU,LFUDA,...) (read_hits) =~ byte_hit_rate (LRU,LFUDA,...) =~ amount of space needed =~ x * (amount_downloaded) (remove_expired_data) =~ (amount_downloaded) over previous time so disk_work = f(amount_downloaded,byte_hit_rate,cache_replacement_policy) To me this speculative analaysis suggests that the load on the disk is a function of the byte_hit_rate and the amount being downloaded, but not of the absolute cache size. So, decreasing the cache_dir size might lower the disk load, but only as it lowers the byte_hit_rate (and possibly the seek time on the disk I guess). Is there something wrong in this? Gavin
