Scrubbing is Ceph's way of verifying that the objects stored in RADOS are consistent, and to protect against bit rot or other corruptions. Scrubbing can either be normal or deep, depending on the set schedule. During a normal scrub operation, Ceph reads all objects for a certain PG and compares the copies to make sure that their size and attributes match. A deep scrub operation goes one step further and compares the actual data contents of the objects. This generates a lot more I/O than the simpler standard scrubbing routine. Normal scrubbing is carried out daily, whereas deep scrubbing is attempted to be carried out weekly due to the extra I/O load.

Despite being deprioritized, scrubbing does have an impact on client IO, and so, there are a number of OSD settings that can be tweaked to guide Ceph as to when it should carry out the scrubbing.

The osd _scrub_begin_hour and osd _scrub_end_hour OSD configuration options determine the window Ceph will try and schedule scrubs in. By default, these are set to allow scrubbing to occur throughout the 24-hour period. If your workload only runs through the day, you might want to adjust the scrub start and end times to tell Ceph that you want it to scrub during off peak times only.

It should be noted that this time, a window is only honored if the PG has not fallen outside its maximum scrub interval. If it has, then it will be scrubbed regardless of the time window settings. The default max intervals for both normal and deep scrubs are set to one week.