2024-09-30T06:48:49.346Z

<Ilya Dryomov> Hi Jon
`rbd_diff_iterate2()` reports based on what was actually written to the OSDs (i.e. what makes it to RADOS before the cluster goes offline in your example)
Your "4MB data block at offset 128" scenario is more involved because the default object size is also 4MB and so such a write would span two RADOS objects which would be written to concurrently
It's likely that by the time 2MB get written to object 0, the remaining 128 bytes would get written to object 1 too and once the cluster is back online `rbd_diff_iterate2()` would report a change in `128~2MB` and `4MB~128` ranges

2024-09-30T06:49:37.054Z

<Ilya Dryomov> If no data is written to offset 128, `rbd_diff_iterate2()` would report nothing, indicating no change

2024-09-30T06:49:58.445Z

<Ilya Dryomov> If no data gets written to offset 128, `rbd_diff_iterate2()` would report nothing, indicating no change

2024-09-30T06:51:12.584Z

<Ilya Dryomov> If no data gets written to offset 128, `rbd_diff_iterate2()` would report nothing for object 0, indicating no change

2024-09-30T06:58:46.998Z

<Ilya Dryomov> Separately, in case that is an actual 4MB data block which is submitted in one go and doesn't get split in any way before it gets to RBD, only the following is possible:
• change in `128~4194176` and `4194304~128` ranges is reported
• change in `128~4194176` range is reported (only write to object 0 makes it)
• change in `4194304~128` range is reported (only write to object 1 makes it)
• no change is reported (neither write makes it)

2024-09-30T07:00:27.299Z

<Ilya Dryomov> Writes that don't span object size boundaries are atomic, so having only 2MB written to object 0 in such a case is impossible

2024-09-30T08:24:57.180Z

<Ilya Dryomov> Separately, in case that an actual 4MB data block is submitted in one go and doesn't get split in any way before it gets to RBD, only the following is possible:
• change in `128~4194176` and `4194304~128` ranges is reported
• change in `128~4194176` range is reported (only write to object 0 makes it)
• change in `4194304~128` range is reported (only write to object 1 makes it)
• no change is reported (neither write makes it)

2024-09-30T15:08:30.820Z

<Laura Flores> Hey all, CDM is happening this week! RSVP here: <https://www.meetup.com/ceph-user-group/events/303725485/>