How to generate a large file allocating space

[Andreas Dilger]

On 2010-10-31, at 09:05, Alex Bligh wrote:
> I am trying to allocate huge files on ext4. I will then read the extents
> within the file and write to the disk at a block level rather than using
> ext4 (the FS will not be mounted at this point). This will allow me to
> have several iSCSI clients hitting the same LUN r/w safely. And at
> some point when I know the relevant iSCSI stuff has stopped and been
> flushed to disk, I may unlink the file.

Hmm, why not simply use a cluster filesystem to do this?

GFS and OCFS both handle shared writers for the same SAN disk (AFAIK), and Lustre uses ext4 as the underlying filesystem, and though it doesn't allow direct client writes to the same disk it will allow writing at 95% of the underlying raw disk performance from multiple clients.

Cheers, Andreas