Thank you Eric. That 'sounds like' exactly my issue. Though I'm surprised to bump into something like that on such a small system and at such low bandwidth. But the information I can find on those parameters is sketchy to say the least. Can you point me at some doco that explains what they do, how to read the current values and how to set them? Cheers, Steve -----Original Message----- From: Eric Smith <Eric.Smith@vecima.com> Sent: Monday, 11 May 2020 8:00 PM To: Steve Hughes <steveh@scalar.com.au>; ceph-users@ceph.io Subject: RE: [ceph-users] Re: Write Caching to hot tier not working as expected It sounds like you might be bumping up against the default objecter_inflight_ops (1024) and/or objecter_inflight_op_bytes (100MB). -----Original Message----- From: steveh@scalar.com.au <steveh@scalar.com.au> Sent: Monday, May 11, 2020 5:48 AM To: ceph-users@ceph.io Subject: [ceph-users] Re: Write Caching to hot tier not working as expected Interestingly, I have found that if I limit the rate at which data is written the tiering behaves as expected. I'm using a robocopy job from a Windows VM to copy large files from my existing storage array to a test Ceph volume. By using the /IPG parameter I can roughly control the rate at which data is written. I've found that if I limit the write rate to around 30MBytes/sec the data all goes to the hot tier, zero data goes to the HDD tier, and the observed write latency is about 5msec. If I go any higher than this I see data being written to the HDDs and the observed write latency goes way up. _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io --