Automatically remove old metadata from disks that are formatted

[selulven]

I recently encountered a situation where RAID5 metadata was still left on a disk -- and was causing trouble -- after the disk had been formatted as a ZFS Storage Pool device. graid5 dump <dev> showed that the RAID5 metadata were causing the graid subsystem to recognize the drive as being part of a RAID5 set -- and the disk's activation triggered a rebuild of the RAID set -- even after it had been formatted and added to a pool.

This is both counter-intuitive and potentially extremely damaging. No one expects data on the disk to persist after a format. It's worse that it triggers further automatic actions to be taken without user interaction or any possibility of intervention. It's especially aggravating that this will likely result in the loss of data on the disk (in my case, a RAID5 being rebuilt on top of a ZFS Storage Pool with a zvol on it).

The consensus in the ZFS sphere seems to be that the user must resolve this manually, on the command line, by dd-ing 4K of data to the start and end of the disk to wipe any residual metadata. As far as targeting users goes, that's bordering on hopeless.

In my opinion, there are no use cases that require metadata from the previous storage system to persist after the disk has been repurposed. This applies regardless of which is the previous and which is the next storage system. Users who format their disks will not and can not expect any of the existing data to persist.

Therefore, I propose that whenever a disk is formatted using the web GUI, the recommended wiping actions (4K start and end, or whatever is considered appropriate) are performed automatically.

[mooblie]

+1
Maybe this is why some disks won't appear in the "Format" GUI menu - a constant problem for me, when trying to build/test different configurations.

[JoseMR]

This should be done automatically indeed, but for manually remove any metadata on disk, the following link could help: http://wiki.nas4free.org/doku.php?id=faq:0129

Below is a sample script to wipe the first and last 100M of selected disk, similar technique Western Digital uses for quickly wipe a miss behaving disk, you can modify the count to anything you need in Blocks.

Code: Select all

#!/bin/sh
# Quick Disk Wiper
printf "\033[31m%s\33[0m\n" "Warning: This will wipe the first and the last 100MB of the selected disk."
echo "What disk do you want to wipe?"
camcontrol devlist
echo "For example - ada0 :"
read disk
printf "\033[31m%s\33[0m\n" "All data on the following disk will be destroyed: $disk!"
echo "Press Enter to continue or CTRL+C to abort!"
read next
echo "Disk wiping started!"
diskinfo ${disk} | while read disk sectorsize size sectors other
    do
        # Wipe the first 100MB.
        /bin/dd if=/dev/zero of=/dev/${disk} bs=${sectorsize} count=204800
        # Wipe the last 100MB.
        /bin/dd if=/dev/zero of=/dev/${disk} bs=${sectorsize} oseek=`expr $sectors - 204800` count=204800
        echo "e." > /dev/speaker
    done
echo "Done!"