NeilBrown wrote:
> On Fri, 09 Jul 2021, Wakko Warner wrote:
> > Reindl Harald wrote:
> > >
> > >
> > > Am 08.07.21 um 23:48 schrieb Wakko Warner:
> > > > I have a raid5 of 3 disks.
> > > >
> > > > 2 of them have bad sectors. Sector 1110 and 1118.
> > > >
> > > > I'm curious to know if these sectors actually contain any data or if they
> > > > can just be overwritten.
> > >
> > > the RAID layer don't know anything about data by definition, it even don't
> > > care what filesystem is running on top
> >
> > So did you actually read what I said?
> >
> > Data Offset : 262144 sectors
> > Super Offset : 0 sectors
> >
> > This is /dev/sda1 which starts at sector 128 of /dev/sda. Sector 1110 on
> > /dev/sda is bad. That would place it between super offset and data offset.
> > Thus, there wouldn't be a filesystem there. I'm asking if it contains any
> > "data" that might be "used" by "something". My /dev/md0 data starts at
> > offset 262144 of /dev/sda1 which is well beyond sector 1110 of /dev/sda.
>
> If you had an unusually large bitmap, it might use those bad sectors,
> but unlikely.
> If you reshaped the array to more devices, it would reduce the Data
> Offset, so might start writing in that space.
>
> Otherwise you should be safe.
Ok thanks. I did do a superblock backup on my 3 drives a few months ago. I
checked offset 72 to offset 262143, it was all 0s. I assume whatever is
there was on the disk and not wiped when I created the array.
I also dumped the same sectors from each of the disks. interestingly, what
is stored there is the same on all 3 drives except for the areas that were
bad.
This array has never been reshaped. It also has never had a disk replaced.
I already DD'd zero to the drive, but only the sectors that were not
readable. Didn't see any reason not to. I found it interesting that the
reallocated sectors didn't go up. The drives have 13 years of power on
time.
This is mdstat:
md0 : active raid5 sda1[0] sdb1[1] sdc1[3]
488018688 blocks super 1.1 level 5, 64k chunk, algorithm 2 [3/3] [UUU]
bitmap: 1/2 pages [4KB], 65536KB chunk
And that is the only array on this machine.
--
Microsoft has beaten Volkswagen's world record. Volkswagen only created 22
million bugs.
