VM's using Physical HDD's and software RAID - error with Windows HOSTS

Hi there
Watch carefully when using physical HDD's with VM (i.e use the Native FS on the whole Disk - without GPT info with file systems such as EXT4 / XFS ) on a WINDOWS HOST.

The problem arises in this type of case :
4HDD's D1 GPT Partitioned C for Windows etc, D as XFS.
D2,3,4 formatted totally XFS. D2,3,4 defined as single RAID 0 array.

Start up the VM.

The raw partition on D1 will stop any changes to partition tables so next time you boot the VM the HDD's will be shown as 4 single HDD's every time you power on the VM.

The RAID 0 array can be re-started without loss of data (you need to re-create it again and not reformat the fs). Just use the mdadm command to redefine the array again and it will start OK.

If you remove the partition D from the VM then everything is fine again so if you want physical HDD's use the entire HDD not a RAW partition. If you need more space then define the partition D as a Virtual HDD -- even though using VHD's lowers performance of the I/O subsystem -- you are probably better off sharing the Windows Native partition with the VM in this case.

Just a little trap for the unwary.

Cheers
jimbo

slicendice said:

Yep this makes sense. You define RAID arrays in real life too using whole physical disks, not partitions. :)

Hi there @slicendice
That partition wasn't part of the array though.

However deleting it from the VM config you can get back your data

......................

[root@hestur jim]# mdadm --create --verbose /dev/md1 --level=0 --raid-devices=3 /dev/sdb /dev/sdc /dev/sdd
mdadm: chunk size defaults to 512K
mdadm: partition table exists on /dev/sdb
mdadm: partition table exists on /dev/sdb but will be lost or
meaningless after creating array
mdadm: partition table exists on /dev/sdc
mdadm: partition table exists on /dev/sdc but will be lost or
meaningless after creating array
mdadm: partition table exists on /dev/sdd
mdadm: partition table exists on /dev/sdd but will be lost or
meaningless after creating array
Continue creating array? y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md1 started.
[root@hestur jim]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 200G 0 disk
├─sda1 8:1 0 1G 0 part /boot
└─sda2 8:2 0 199G 0 part
├─cl-root 253:0 0 50G 0 lvm /
├─cl-swap 253:1 0 2G 0 lvm [SWAP]
└─cl-home 253:2 0 147G 0 lvm /home
sdb 8:16 0 3.7T 0 disk
└─md1 9:1 0 9.1T 0 raid0
sdc 8:32 0 2.7T 0 disk
└─md1 9:1 0 9.1T 0 raid0
sdd 8:48 0 2.7T 0 disk
└─md1 9:1 0 9.1T 0 raid0
sr0 11:0 1 1024M 0 rom
[root@hestur jim]# mount /dev/md1 -t auto -o rw /mnt/DV2

Now all my data is back and on re-boot the RAID array is there again



Don't do any re-formatting or you will lose data.

Cheers
jimbo