Playing around with software raid17 Oct 2006
And you don’t even need any physical disks for it….
I don’t use Linux software raid tool
mdadm that often so I quickly forget how it works. This is something I used on several occasions, when trying to refresh my mind. The cool thing is that you don’t need physical disks or a lot of space for it to work. The following might vary a bit depending on you system (mine is Ubuntu Edgy Eft on IBM x40).
First create a few “disks”… by creating some empty files and making them into block devices:
dd if=/dev/zero of=disk1 bs=1M count=1 seek=30 dd if=/dev/zero of=disk2 bs=1M count=1 seek=30 dd if=/dev/zero of=disk3 bs=1M count=1 seek=30 losetup /dev/loop0 disk1 losetup /dev/loop1 disk2 losetup /dev/loop2 disk3
This creates 3 files (
disk3) with the size of 1MB in the current directory and makes them into block devices (just like normal disks is).
Now create your raid, example:
mdadm --create /dev/md0 --level=5 --raid-devices=2 --spare-devices=1 /dev/loop0 /dev/loop1 /dev/loop2
If you get the error:
mdadm: error opening /dev/md0: No such file or directory
Add the parameter
--auto=md to the raid create command.
Now you can see you raid status with:
Now play around with it all you want
When you are done you stop the raid and remove it with the following:
mdadm --stop /dev/md0 mdadm --remove /dev/md0
Perhapes you want to remove the
md0 device again with (only if you needed the
Cleanup the “disks”:
losetup -d /dev/loop2 losetup -d /dev/loop1 losetup -d /dev/loop0 rm disk3 rm disk2 rm disk1
Now you computer wont have a trace of you your software raid disks… besides you shell history :)
Playing around with software raid by Jacob Emcken is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.