[Lustre-discuss] creating and using loopback device on a file on a lustre filesystem?

[Andreas Dilger]

On 2009-12-05, at 16:13, Richard Lefebvre wrote:
> Would it be safe to create a file on a lustre file system and use it  
> as
> a loop device for mounting?
>
> Sort of doing something like this (creates a 100G file):
>
> mount -t lustre msdserver at o2ib0:/lustre /mnt/lustre
> dd if=/dev/zero of=/mnt/lustre/myfsfile bs=1024 count=104857600
> mkfs.ext3 /mnt/lustre/myfsfile
> mkdir /mnt/myfs
> mount -o loop /mnt/lustre/myfsfile /mnt/myfs


You mean like sanity.sh test 54c does?  Yes.  However, I'm not totally  
sure that ext3 on top of a loop device is "safe", regardless of  
whether this is Lustre or not.

Some users do this (with ext2) to have a node-local mechanism for  
accessing a lot of small files.  It is also possible to use such  
loopback files in read-only mode (again with ext2 only) from many  
nodes at one time.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.