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I have a mdadm software raid 1 on external disks with media data.

For travel I want to take the data with me.

I imagine to set the raid and the underlying filesystem in readonly mode and take just one disk with me. Is this possible?


I tried to

mount -o ro /dev/sdc1 /mnt/test

mount: unbekannter Dateisystemtyp „linux_raid_member“

So the partition type is Linux raid autodetect (the raid array is partitioned altogether as reiserfs


having written the task, helped me to clear my mind. I think I have to run the same mdadm configuration in my laptop and just do a mdadm remove onedisk and mount the array like that and readonly. Any comments please?

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Try it. If it works post it as an answer here and get som rep for it. – Nifle Aug 4 '12 at 12:26
up vote 0 down vote accepted

Here's what I did :

I copied the mdadm.conf to the laptop. But later removed that and did on that box a fresh

mdadm --detail --scan >> mdadm.conf

I don't know very much about the md device auto numbering: md127 when and why; If the name stored on the array; If the metadata has to match etc.

Anyway - I continued: Plugged both disks and checked if array is active and both disks fine; Watched syslog so I saw which physical disk is which device.

Then marked as read-only, but found out I cannot mark disk as failed / remove disk in ro state so I remarked as rw


mdadm /dev/md0 -f /dev/sdc2
mdadm /dev/md0 -r /dev/sdc2

Plugged off that disk I removed. ( I have one disk pair with two arrays on it - I had to care to do these steps for both arrays and then plug off; Another 2TB disk pair with one array was simpler )

Tested mounting / unmounting / plugging-off / replugged / mount - as root and via palimpsest : It asks if one wants to mount array in degraded state. - "Yes" and fine

Just not sure if mount points will be fine. Once I had the msg , mount point is missing - i created them manually

Good luck to anyone doing same thing. And good luck to me, re-assembling the arrays at home again in four weeks ... ;-) -

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