[Ukfreebsd] File System Ext2 On DVD+RW

RW rwmaillists at googlemail.com
Sun Dec 21 19:37:49 GMT 2008

On Sat, 20 Dec 2008 18:49:45 +0000
Frank Mitchell <mitchell at wyatt672earp.force9.co.uk> wrote:

> Hi:
> Recently I noticed Sun Solaris used CDs with a UFS File System. So I
> decided to try UFS and Ext2 on Optical Disks. It should work on
> CD-RW, but I had spare DVD+RW disks, so I decided to get more
> ambitious.
> Note that DVDs use 2048-byte Sectors like CDs, but they're handled in 
> Error-Correcting Blocks of 16. You can't expect DVD-RW to work,
> because DVD-RW only writes complete ECC Blocks. But DVD+RW (like
> DVD-RAM) can update individual Sectors.
> FreeBSD UFS1 wouldn't work this way.

I've never tried it myself, but I'm pretty sure some said he'd used
DVD+RW with UFS2 and even geli encryption.

> Does anybody have thoughts about this idea? Like: Any disadvantages
> which haven't occurred to me? Obviously if you're recording Personal
> Information on Removable Media it might be preferable to use a format
> which isn't readable under  Windows.

I think geli-encrypted memory stick are more convenient if you want
secure RW access. However, it's quite easy to burn geli-encrypted DVDs
by putting your data on a vnode md device (2k sector size), and then
burning the backing file as if it were a normal DVD ISO file. 

On Sun, 21 Dec 2008 17:55:09 +0000
Frank Mitchell <mitchell at wyatt672earp.force9.co.uk> wrote:

> I discovered the disadvantage of putting an Ext2 File System on
> DVD+RW: FreeBSD and NetBSD can't mount it, even though they're fine
> with Ext2 on a Hard Disk partition.

That's bit surprising, I'm pretty sure you can mount ufs2 DVD+/-R and
I'm certain you can with geli.

Are you sure it's not an inode size problem. FreeBSD has a problem
mounting recently created ext2 partitions. I think you have to override
the default even on FreeBSD's own tools.

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