MD devices are not wiped if LVM exists

[tt-fai at kky.ttu.ee]

Hello,

 

I have, for a long time, had a separate FAI action around, which I call “cleandisks”. This makes re-installing a lvm- and/or raid-equipped host a two stage process:

1) Boot into FAI_ACTION=cleandisks. Let the script wipe the disks.

2) Reboot into install. During this boot, the kernel should find clean disks and not make any assumptions about earlier states of the disks.

 

The functionality of the script is similar to that of Andrew's WIPEDISKS, but let me copy it here (with some sanitation) for reference:

 

case `hostname` in

    some_sample_host)

        # This needs to be set up for each host, by looking at its configuration prior to reinstall.

        # Non-existent disks, partitions, etc, will not hurt in most cases, so better err in the direction of too many.

        LV_LIST="lv1"

        MD_LIST="md0 md1 md126 md127"

        DISK_LIST="sda sdb"

        PART_LIST="sda1 sdb1 sda3 sdb3"

        ;;

    […]

esac

 

lvdisplay

 

# Repeat all this twice!

for round in 1 2 ; do

 

    for LV in $LV_LIST

    do

        vgremove -f $LV

    done

 

 

    for MD in $MD_LIST

    do

        mdadm --remove /dev/$MD

        mdadm --stop /dev/$MD

    done

 

    for PART in $PART_LIST

    do

        mdadm --zero-superblock /dev/$PART

        mdadm --zero-superblock /dev/$PART

    done

 

   for DISK in $DISK_LIST

    do

       dd if=/dev/zero of=/dev/$DISK bs=10240 count=100000

    done

 

done

 

lvdisplay

 

 

This is a lot of overkill, and some of the commands fail, especially on the second round, but this way I have always got rid of all the old data on the disks and booted into a problem-free reinstall.

 

Hoping this helps,

Toomas

 

 

From: linux-fai <linux-fai-bounces at uni-koeln.de> On Behalf Of Jerry Steele
Sent: teisipäev, 2. juuli 2019 15:08
To: fully automatic installation for Linux <linux-fai at uni-koeln.de>
Subject: Re: MD devices are not wiped if LVM exists

 

Moving away from Andrew's WIPEDISKS script for a second, I have made a simple script containing just

 

vgdisplay

 

The output from this is null, suggesting that FAI does not see any LVM stuff at this stage, however after it has completed these bits of the disk_config,

 

Executing: wipefs -af /dev/sdb1
Executing: wipefs -af /dev/sda1
Executing: wipefs -af /dev/sdd1
Executing: wipefs -af /dev/sdc1
Executing: mdadm --stop --scan
Executing: mdadm --assemble --scan --config=/tmp/fai/mdadm-from-examine.conf
Executing: mdadm -W --stop /dev/md0
Executing: mdadm -W --stop /dev/md2

 

... the LVM volumes are visible again (I can't grab the ouput of "vgdisplay", but it shows the volume groups). I'm guessing that this shows that the LVM metadata is immune to the wipefs stuff.

 

I have to stop looking at this for the moment, but I'll see if I can pick it up later and report back (unless anyone else has come across this and can report back, of course)

 

Thanks for your help so far guys..

 

-- 

---

Jerry Steele
Telephone: +44 (0)7492 910225

GPG: 43A3A8C6

 

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