I have a server which has two 256GB SSDs. They were partitioned as following:

/dev/sda1 100GB linux-raid-autodetect
/dev/sda2 100GB linux-raid-autodetect
/dev/sda3 23,6GB linux-raid-autodetect

/dev/sdb1 100GB linux-raid-autodetect
/dev/sdb2 100GB linux-raid-autodetect
/dev/sdb3 23,6GB linux-raid-autodetect

There were 2 raid1 - devices build and running (using mdadm):

/dev/md1 (built of /dev/sda2 and /dev/sdb2) containing an ext4 filesystem mounted on /
/dev/md2 (built of /dev/sda3 and /dev/sdb3) containing swap filesystem

/dev/sda1 and /dev/sdb1 were used in former times and now are unused.

So I want to remove both unused partition /dev/sdx1 and grow /dev/sdx2 to double size (200GB).

I have proceeded as following:

mdadm --manage /dev/md1 --fail /dev/sda2
mdadm --manage /dev/md1 --remove /dev/sda2

Then I entered fdisk, deleted /dev/sda1 and /dev/sda2 and created one new partition /dev/sda2 which now uses the complete free spave of former /dev/sda1 and /dev/sda2. I set partition identifier to linux-raid-autodetect (fd) and wrote partition table to disk. After doing so I readded /dev/sda2 to /dev/md1 with

mdadm --manage /dev/md1 --add /dev/sda2

and waited for raid syncing finishes. Everything worked as expected. The result is a new /dev/md1 which consists of /dev/sda2 (200GB) and /dev/sdb2 (100GB). Now I proceeded as before with /dev/sdb. After the complete procedure I got partitioning of SSDs as following: /dev/sda2 200GB linux-raid-autodetect /dev/sda3 23,6GB linux-raid-autodetect

/dev/sdb2 200GB linux-raid-autodetect
/dev/sdb3 23,6GB linux-raid-autodetect

and these are part of the same RAID1 /dev/md1 and /dev/md2) as before. Both RAID are running fine. The untouched /dev/md2 is perfectly, but the new /dev/md1 is showing only 100GB (half the space which is in theory available). Of course: raid device needs resized to maximum capacity and filesystem (ext4) must be resized after doing that. So I started

mdadm --grow --array-size=max /dev/md1

...but this has absolutely no effect. The following

resize2fs /dev/md1

results in "Filesystem is already 26198016 (4k) blocks long. Nothing to do!"

What is the problem? I have worked with the system on /dev/md1 so it is mounted. Must I resize raid and filesystem with a rescue system (/dev/md1 not mounted)? Or is there a mistake I am doing?

  • 1
    Did the kernel actually re-read partition table and accept the new partition size? Otherwise it's possible the sda2 you re-added was the same old 100GB one. If you didn't reboot, check lsblk, cat /proc/partitions, ... Also check mdadm --examine for these partitions, it should show device size, offsets, etc. Aug 28, 2023 at 6:10

1 Answer 1


I have fixed it in the meantime. Syntax for mdadm grow was wrong. It must be

mdadm --grow /dev/md1 --size=max

If I do so I can resize array and after that resize filesystem. This all works without reboot and at mounted filesystem.

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