Hi Magnus, Here is the brief overview for the relevant perf counters: - 'issued deferred writes' denotes amount of user write ops which have got deferred processing and have been persisted at Key-Value DB (The first stage of deferred write procedure). - 'submitted deferred writes' denotes amount of writes which have been submitted to main device to reach their final disk location. (the second stage of deferred write procedure). Additionally there is the last stage which is staged deferred writes cleanup from KV. But there is no relevant counter to track this state though at the moment. Frankly speaking I recall no modifications to bluestore_prefer_deferred_size_hdd happened to Squid. The only not-that-recent PR which might look relevant is https://github.com/ceph/ceph/pull/48490 but it's been backported back to Pacific and Quincy. May be you had had another upgrade(s) prior to R->S one recently which triggered the regression? It would be great to get more information on the issue including perf counter dumps and more details on that performance degradation and write patters which are affected. Thanks, Igor On 4/14/2026 5:00 PM, Magnus Grönlund via ceph-users wrote:
Hi All,
We are running a 5 year old 15 node Ceph cluster with spinners for data and NVMe for DB/Wal. After the recent upgrade to Squid (from Reef) some users reported issues with fluctuating (often bad) disk performance especially affecting k8s etcd. They point to the change to bluestore_prefer_deferred_size_hdd claiming that it's detrimental to the "synchronous write patter" of escd. They also point to submitted_deferred_writes and issued_deferred_writes claiming that there is a massive and growing backlog of deferred writes.
I'm not 100% correct that this is the issue but I'm having a hard time finding any relevant information (bad google-fu?) especially about what submitted and issued deferred writes actually represents and why the difference between issued - submitted keeps growing. Anyone got some insights to share?
Thanks in advance Magnus _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io