Hi,
If i have a snapshot origin created using dmsetup create table with a mapping real device with (major,minor) =(8,18) and lets name it /dev/mapper/dmso . Now the set of reads are writes done from /dev/mapper/dmso have some values (R,W).
Had i been creating a persistent snapshot using (P or PO) mode with origin device as /dev/null and COW device is my real device (maj,min)=8,18 and it is named as /dev/mapper/dmsp. Now if i do the exact same reads and writes that i did to dmso (snapshot-origin) , will get i the same set of output values (R,W).
In my experiment i did. So i'm asking is there a case where it differs ?
Also i looked at the code in drivers/md/dm-snap.c and i find that both the drivers snapshot and snapshot-origin use the same __orgin_write . So my partial/incomplete understanding is that it works from the read/write view point from /dev/mapper/dmsp.
I'll not be using the snapshot-merge feature , so merging to /dev/null is irrelevant here.
Regards,
-- Navin
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