one ripple effect of multi-instance cassandra will be on graphite metrics, ATM each cassandra JVM uses ~11G on disk in graphite, e.g. restbase1009 (total 222G now)
per-CF metrics take up two-three order of magnitudes more than the rest
$ du -hcs restbase1009/org/apache/cassandra/metrics/* 1.5M restbase1009/org/apache/cassandra/metrics/CQL 12M restbase1009/org/apache/cassandra/metrics/Cache 46M restbase1009/org/apache/cassandra/metrics/ClientRequest 9.9G restbase1009/org/apache/cassandra/metrics/ColumnFamily 9.9M restbase1009/org/apache/cassandra/metrics/CommitLog 2.4M restbase1009/org/apache/cassandra/metrics/Compaction 47M restbase1009/org/apache/cassandra/metrics/Connection 14M restbase1009/org/apache/cassandra/metrics/DroppedMessage 3.6M restbase1009/org/apache/cassandra/metrics/FileCache 4.5M restbase1009/org/apache/cassandra/metrics/ReadRepair 1.2M restbase1009/org/apache/cassandra/metrics/Storage 38M restbase1009/org/apache/cassandra/metrics/ThreadPools 10G total
and some metric types have plenty of derived metrics which contribute to that, e.g. latencies CasCommitLatency
-rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:50 15MinuteRate.wsp -rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:49 1MinuteRate.wsp -rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:49 50percentile.wsp -rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:49 5MinuteRate.wsp -rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:51 75percentile.wsp -rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:49 95percentile.wsp -rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:50 98percentile.wsp -rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:50 999percentile.wsp -rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:47 99percentile.wsp -rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:47 count.wsp -rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:47 max.wsp -rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:48 mean.wsp -rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:49 meanRate.wsp -rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:50 min.wsp -rw-r--r-- 1 _graphite _graphite 309088 Sep 25 13:50 stddev.wsp
for each of those there's between 2k and 3k files each of 309kb
15MinuteRate.wsp:1389 1MinuteRate.wsp:1389 50percentile.wsp:2141 5MinuteRate.wsp:1389 75percentile.wsp:2141 95percentile.wsp:2141 98percentile.wsp:2141 999percentile.wsp:2009 99percentile.wsp:2141 count.wsp:3548 max.wsp:2141 mean.wsp:2009 meanRate.wsp:1389 min.wsp:2141 stddev.wsp:2009
I think we can trim the list of derived metrics to the most relevant ones, e.g. 50/75/95/99 percentile, count, 1MinuteRate