On 26/01/2019 11:49, Harald Dunkel wrote:
I initiated a check of my RAID1 (2 disks) this morning. mismatch_cnt
is at 128 by now.
AFAIR 128 is a rounded number, and you are not going to get it more
precise than this.
It depends on the granularity of the check, which depends on the raid1 code.
There is no official way to do what you want.
You have to write a software in a generic programming language, to
compare sector-per-sector (actually 4k granularity is the smallest you
can go) the two underlying MD devices.
Since the array modifies while you check it, perform the check twice and
"AND" the two results together, so to get the mismatches that happened
on both checks.
You have to skip the MD header at the beginning and/or at the end,
because it is going to be mismatched, and also in order to compute the
offset precisely.
Then, if you want to publish your software... :-)
These mismatches happen, in raid1, but why they happen is not precisely
known. There are a few ideas... and it is said that they are harmless in
most cases (=outside of files).
The phenomenon happens a lot less if you have LVM over the raid1, and
also this is not exactly known why.
It doesn't seem to happen in raid5/6.
Can't remember about raid10.
After you have the offset, it is like you say: use debugfs.
If you do the check, let us know ...
good luck
