Re: /dev/md0

[Philippe Troin <phil@fifi.org>]

On Thu, 09 Oct 1997 14:26:02 +0200 Pere Camps (pere@casal.upc.es) 
wrote:

> 	I have a linear partition on my linux box (/dev/md0 =
> hdb7+hdb9+hdb11), and when I run the `mdadd -ar`, and I then mount the
> filesystem something like the following comes up:
> 
> 	Warning: /dev/md0 has no checksum field
> 	
> 	Should I worry?

Yes and no.
This is because you created you mdtab by hand, and not with mdcreate.
Mdcreate computes a checksum and puts it in the mdtab.
When mdrunning a md partition, the checksum is computed and is compared to the one stored in the mdtab. If they're different, the md device isn't started.

Having checksums can prevent you major problems if for example you add new disks and the devices change:
	You have /dev/sda1 and /dev/sdb1 as a single MD disk.
	/dev/sda has SCSI ID 0, /dev/sdb has ID 6.
	You add a new scsi device with id 3.
	Your /dev/sdb becomes /dev/sdc !
	You'll probably trash your md device on next mount...
The same can happen if you add/delete partitions...

So, to have this checksum added to your mdtab, recreate it with mdcreate.

Phil.

	


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