Create a new volume on free diskspace from inside Dom0

Question

I have a server with two HDDs (/dev/sda and sdb) with 1.8TB each.

On both disks, there is a 500MB Swap and an 800GB partition, that are in a raid md0 and md1:

pvs
  PV         VG   Fmt  Attr PSize   PFree 
  /dev/md1   vg0  lvm2 a--  799,87g 63,87g

I am root in Dom0 and created a new partition /dev/sda3 in the former free space with cfdisk. Now it looks like:

Device     Boot      Start        End    Sectors  Size Id Type
/dev/sda1             2048    1050624    1048577  512M fd Linux raid autodetect
/dev/sda2          1052672 1678774272 1677721601  800G fd Linux raid autodetect
/dev/sda3       1678776320 3907029167 2228252848    1T 83 Linux

I want to use this free space as backupspace, so I don't want a raid here, but I cannot create a filesystem on /dev/sda3 now:

$ mkfs.ext4 /dev/sda3
mke2fs 1.42.12 (29-Aug-2014)
The file /dev/sda3 does not exist and no size was specified.

And it doesn't appear in

# ls -l /dev/sda*
brw-rw---- 1 root disk 8, 0 Mai 24 22:07 /dev/sda
brw-rw---- 1 root disk 8, 1 Mai 24 22:07 /dev/sda1
brw-rw---- 1 root disk 8, 2 Mai 24 22:07 /dev/sda2

How can I create a non-raid filesystem now in /dev/sda3?

Answer 1

You need to tell the kernel that the partition table has changed after you make any changes to partition tables with fdisk, cfdisk, or parted etc.

There are two main ways of doing this:

1. Reboot. The kernel will detect the new partition table and use it automatically.

2. run partprobe as root. This will tell the kernel to scan the block-device partitions and update its internal partition table records.

   partprobe is in the parted package. apt-get install parted

Until you do this, there will be no device node for the new parition(s) in /dev, so you will not be able to run mkfs to format it.