Re: [9fans] writable optical media

Re: [9fans] writable optical media

[rob pike]

We did this a couple of years ago by doing raw copies of the media.
It worked fine.  JMK might be able to give you more information.

-rob

Re: [9fans] writable optical media

[Martin Harriss]

presotto@plan9.bell-labs.com wrote:
>
[ stuff deleted... ]
>
> I guess the moral is: optical is nice, but when the lifetime of
> each round of technology is around 5 years, you have to recopy
> every few years anyways since the devices to read the indestructible
> media atrophy.  Also, the density goes up fast enough that
> copying every few years means that you can always have everything
> on line.

Has anyone done any work on integrating "old dumps" into a new file
server?  I know the dumps are supposed to be immutable, but it would be
nice to set up a new file server using the latest technology and be ably
to migrate one's old dumps seamlessly into the new server.  This would
be particularly useful when migrating to a bigger dump device.  Can this
maybe be done just by copying the data and then fudging the size in the
superblock?

Martin

Re: [9fans] writable optical media

[Matt]

i think the quoted medi life for pre-preinter silver disks
(pre-pressed cd roms) is around 10 years.

"golds" is somewhat less

photons wear them out so keep them in a dark lead cupboard

TDK quotes > 10^8 reads for 128Mb MO disks

they don't show figures for cd roms

[9fans] writable optical media

[presotto]

We still have optical media from the start of the project that
is readable.  However, I have no idea how long this media lasts.
Anyone out there know what the record is?  It seems to me the
technology for manufacturing the media changes quickly
perhaps to get price down.

I do know that, as usual, when going back to read old stuff
we found a bunch of implementation errors that caused us to
write part of file A in the middle of file B.  Largely it
was us not understanding the Sony jukebox.  It was interesting
to see vc core dumping because a piece of dennis' mailbox
was embedded in the binary.

Seanq recently copied all our old media into his new compressing
file system and managed to get most of it.  The hardest part
was not the media but the slowly dying previous generations of
optical devices.

I guess the moral is: optical is nice, but when the lifetime of
each round of technology is around 5 years, you have to recopy
every few years anyways since the devices to read the indestructible
media atrophy.  Also, the density goes up fast enough that
copying every few years means that you can always have everything
on line.