Re: [Qemu-devel] PATCH: Support for multi-file raw images

[Troy Benjegerdes <hozer@hozed.org>]

On Thu, May 11, 2006 at 02:30:45AM -0400, Ryan Lortie wrote:
> Hello.
> 
> Attached is a C file (and small patch) to add support for multi-file raw
> images to QEMU.  The rationale (for me at least) is as follows:
> 
> I use rsync to backup my home directory.  The act of starting up QEMU
> changes a 20GB file on my drive.  This causes 20GB of extra copying next
> time I do backups.  If I could split the drive image into smaller parts
> (maybe 2048 10MB files) then the amount of extra copying is drastically
> reduced (since only a few of these files are modified).
> 
> There are definitely other reasons that this may be useful.

Have you tried making a read-only 'base' image and using qcow images
instead? I'm not convinced that splitting things up is going to help a
lot. You might end up writing 1 512 byte block each to 500 files.. in
the qcow image case, that is writing 256K, and with 10mb files, that's
5GB.

>  o If the files comprising the device are deleted (for example) while
>    QEMU is running then this is quite bad.  Currently this will result
>    in read/write requests returning -1.  Maybe it makes sense to panic
>    and cause QEMU to exit.
> 

at the very least, the console should print an error. If you can keep
all the files open, deleting the file won't be a problem.