We're noticing some interesting patterns in collectd / librrd is flushing RRD 
files to disk. 

We have a 1TB volume for RRD files, which is at 75% capacity. Over the last few 
weeks the response time of the disks has slowly degraded, with a few sudden 
jumps (see graph below). When it jumps up in response time, it seems collectd 
responds by halving the write ops, and octets. Is it just deciding to flush 
half as often? If anyone has some pointers to the details of this behaviour, 
that'd be great. 

Also, does anyone recognise this pattern as being related to how full the SSD 
backed volume is, and perhaps the disks are now needing to do garbage 
collection? I'm pretty new to SSDs, and I suspect RRDs are a fairly uncommon 
way to utilise SSD drives. 

FWIW, we have 5 x 256 GB Micron SSDs in a IBM hardware RAID 5 set. The OS is 
linux (ubuntu 12.04). 

disk time, ms: 

bytes per second: 

RRD filesystem disk utilisation: 

Thank you!

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