Read-Only RAID-5 on DVD? :-)

[ubuntu at rio.vg]

Harijs Buss wrote:
> On Monday 03 July 2006 02:25, ubuntu at rio.vg rakstija:
> 
>> Moreover, you'd need a single machine with at least 3 DVD-ROM 
>> drives to read the disks,  which rather cuts down on their usefulness.
> 
> Nope, files might be assembled reading sequentially each DVD, just like p2p 
> programs are assembling files as different fragments arrive.
> 

You'd need to write a special RAID design specifically for it.  Swarming
P2P apps require a special file with the control information and md5sum.
 A normal Raid5 has the filesystem written across the raid, so without
immediate access to n-1 disks, you don't know what sectors to find the
file to reconstruct.  So you'd have to write an entirely new raid5
system that also kept file information on all disks.

It'd require a massive amount of work to do at the filesystem level for
benefits that are miniscule.

Blank DVDs are cheap.  Why not just make two copies?

It'd be possible to write a more user-level app to simulate it.  Like
the P2P apps you mentioned, they could split a file into three or four
parts, and keep the control info right in the file.

I've never heard of such a program, the call for that sort of thing
isn't very high.  Half the point of raid5 is the read speed benefits,
which this system would completely lack, of course.  You'd also lose
quite a bit of convenience...