alain williams wrote on 1/22/26 11:01 AM:
On Thu, Jan 22, 2026 at 10:03:11AM -0700, D. R. Evans wrote:
Due to a cascading series of failures (some of hardware, some of my brain),
I find myself in the following situation:
You do not say what sort of RAID you are using, but you have 2 disks so I
assume RAID-1 (mirrored disks).
No matter how careful I am, I always end up leaving out important information
when asking questions :-)
Yes, you are correct: RAID-1.
I also assume that you have a root file system that is a primary disk
partition, ie you do not use LVM.
I don't use LVM.
The command "parted -l" gives:
----
Model: ATA HGST HDN724030AL (scsi)
Disk /dev/sda: 3001GB
Sector size (logical/physical): 512B/4096B
Partition Table: msdos
Disk Flags:
Number Start End Size Type File system Flags
1 1049kB 16.0GB 16.0GB primary boot, raid
2 16.0GB 2000GB 1984GB primary raid
----
All the system info is in that second partition. I don't rightly recall why
the first partition is present (it's been an awfully long time since I
installed this disk). I suspect that it's reserved for swap, although I doubt
that swapping has ever occurred.
This means that the root filesystem is /dev/sda2, rather than /dev/sda1 as you
assumed.
The easiest way to recover is to boot from a bootable Debian USB memory stick
or CD-ROM. Do not try to rescue, do something like below - needs work at the
command line.
I had a spare hard drive on which I installed a pristine copy of trixie (on
ext4), and that's what I've booted from.
Boot the machine to give you a desktop.
OK.
Open a terminal, become root
OK.
Identify the hard disk that contains your system, look at /proc/partitions.
By "the hard disk that contains your system", I assume you mean the RAID disk.
----
major minor #blocks name
2 0 4 fd0
8 16 1953514584 sdb
8 17 1945125888 sdb1
8 18 1 sdb2
8 21 8385591 sdb5
8 0 2930266584 sda
8 1 15624192 sda1
8 2 1937889280 sda2
11 0 1048575 sr0
11 1 1048575 sr1
9 126 1937757184 md126
----
sdb (size 2TB) is the drive from which I booted. sda (size 3TB) is the old
RAID drive.
I am going to assume that it is /dev/sda with the root file system as /dev/sda1
Actually, /dev/sda2 (see above).
But should I be using /dev/sda2 or /dev/md126 (as listed in /proc/partitions)??
mkdir /tmp/RFS
OK.
mount /dev/sda1 /tmp/RFS
mount /dev/sda2 /tmp/RFS
OK.
For kicks, I also tried
mount /dev/md126 /tmp/RFS
and that also worked fine.
Copy /dev/ to /tmp/RFS/dev/
So here I have a question. This looks like it will try to copy the /dev/ from
the running OS (i.e., the non-RAID drive) and overwrite the /dev that is on
the RAID disk.
Why would one do that? The /dev that was on the RAID disk worked fine until
the other drive of the pair failed; so why does it need to be overwritten by the
/dev from the running system?
I'm sorry if I'm being dense. In this situation, I'm very nervous about
running commands whose purpose I don't understand.
Doc
--
Web: http://enginehousebooks.com/drevans
