Odd cache behavior

Jim Ohlstein jim at ohlste.in
Fri Oct 2 21:07:24 MSD 2009


I'm seeing odd disk usage statistics for my cache. The cache is 
primarily of small files (images, javascript, and css) and sits on a 
128GB SSD using ext2 file system mounted with "noatime" option. The 
cache is all that the the drive is being used for at this time.

The attached graphs were generated by Munin using df. The data from du 
correlates closely with df when run manually.

As you can see, periodically, with no set interval, disk usage rises 
gradually, and then drops precipitously. I don't see anything out of the 
ordinary in the error log. The cache serves about 2.8-3 million requests 
per day, up from ~2.2-2.4 million one month ago.

The cache config is:

fastcgi_cache_path /falcon/cache levels=1:2 keys_zone=one:1024m 
inactive=1d max_size=80g;

where the SSD is mounted as /falcon.

Jim Ohlstein
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