Hello, my question was regarding the use of CD-R's on DEC Alpha Unix
with interoperability on Mac's and PC's as well.
here it is:
I'm sure many of you do this, but I'm looking for info on writing
CD-R's from DEC Alphas, to be used for cheap backups. (since they're
about $1/disk)
1) What software do I need
2) which CD-R recorders are good for DEC's (or does it matter?)
3) are there features the drive needs to have in order to write Unix
directories? (format, etc?)
4) What do I need to do in order for the files be readable on Mac's and PC's.
5) Can I write incrementally or do I have to write all at once?
6) any other gotcha's or things I should know before I buy one?
and here are some of the answers I got. Many thanks to all who answered,
whether I replied personally or not. Y'all are great!
Chester Liu
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From: Lucio Chiappetti <lucio_at_ifctr.mi.cnr.it>
> 1) What software do I need
We have a s/w called GEAR by Elektroson BV (I believe it's a Philips
subsidiary). Actually we run that on Sun, but it is available also for
Alphas and I know other institutes which use it there.
> 2) which CD-R recorders are good for DEC's (or does it matter?)
no idea. We have a Philips one on Sun. Check those supported by the
s/w you will use.
> 3) are there features the drive needs to have in order to write Unix
> directories? (format, etc?)
the physical layout of the CDs is described by a set of industry
standards called the coloured books.
The GEAR s/w won't write CDs which are formatted as Unix filesystems
(i.e. plain ufs mount, like the CDs you use to install the OS), but
in the ISO High Sierra / Rock Ridge formats (mount as cdfs, or hsfs,
according to Unix, which is the most popular standard, in which most
CDs around are written).
> 4) What do I need to do in order for the files be readable on Mac's and PC's.
If you use such format, it will be compatible with PCs. Do not know
anything about Mac. Anyhow the ISO standard has a set of variants for
file naming (from old plain DOS 8.3 filename.typ to other). The most
convenient is the Rock Ridge extension (the -rrip option in the DU mount
command), which keeps a mapping of Unix filenames and permissions. The
CD *appears* as an Unix disk to you.
If the PC does not support it, you will see other file names. The old
version of GEAR we have shows both file names (and actually some commands
use ISO, some other RR-Unix names).
If you have a Windows NT system you know what I mean (go to file manager
and show all file characteristics, you'll see both names !)
> 5) Can I write incrementally or do I have to write all at once?
The GEAR s/w supports multi-session writing (see the coloured book
documentation), but as far as I know no Unix system supports it. So
you won't be able to read what you've written.
Better wait when you have enough data to fill a disk (or significant
fraction thereof)
> 6) any other gotcha's or things I should know before I buy one?
Our docs insist of the importante to write to the CD-R at a constant
speed. If the data transfer speed is faster, won't mind. The s/w
protocol will buffer and force to wait. But if data come too slowly,
while the CD is rotating at fixed speed, a data underrun situation
occurs, and in this case the disk will be useless.
GEAR provides two ways to test this beforehand. One is a software
simulation. The other one sends the data to the CD-R, and puts this
is a simulation mode (test communication link but do not burn CD).
If either test is unsuccessful, you should resort to a physical image.
I'll clarify.
With GEAR you run a first phase in which you list directories and files
to be copied. They can be anywhere on your disks (even NFS). This creates
a virtual image, i.e. just a map.
If you write from virtual image, the actual copy takes place only when
you burn the CD. Speed can be ragged if the files come from NFS disks
sparse anywhere on your LAN.
With a physical image you first create a single file which is an image
of the entire CD, and then copy *that* to the optical disk. You need
600 MB of disk space. This seems to work both with a local disk (local
on the same machine where the CD is) or with an NFS disk.
In general it is advised to have the CD-R on a separate SCSI bus w.r.t
the disks. We have it on a second SCSI where also tape drives are, but
*avoid* using tapes while we are writing CDs.
We've experienced problems writing "nearly full" CDs ("fixation errors",
data are transferred but CD is not closed properly and unusable).
Ah, writing CDs can be slow, blank CD's are given in "minutes" (they are
the same for audio, you know), and it takes more than 1 hr to write 600 Mb
(but we use the 1x speed to write ...)
If you intend to run "production" CDs, you'd better dedicate a w/s to that.
If you want to backup occasional data (as I do, I receive satellite data on
tape, and file them to magnetic disk, and when I run out of space, I archive
them to CD), you can go via NFS and a physical image.
I've also noticed that USING CDs is instead quite fast. I notice no hindered
performance in reading my data directly from mounted CDs instead than from
local or NFS disks.
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From: "K. M. Peterson" <KMP_at_wi.mit.edu>
One question is whether you want "real backup" software -- depending on how you
look at things, you may find that backup software that fits your needs might not
be able to easily or at all write to CD-ROM. For example, we use NSR (NetWorker
)
for backups; I don't think it will write to CD-ROM.
> 2) which CD-R recorders are good for DEC's (or does it matter?)
>
That being said, we're using hardware/software from a company called "Young
Minds" (yes, it know it sounds weird). You may want to check out their site at
http://www.ymi.com .
> 3) are there features the drive needs to have in order to write Unix
> directories? (format, etc?)
>
This is mostly software dependent. Generally, we use a format called
"Rock-Ridge", which allows us full functionality by mounting the CD-ROM with the
options "-r -t cdfs -o rrip".
> 4) What do I need to do in order for the files be readable on Mac's and PC's.
>
Both systems natively support Rock-Ridge as far as I know (we've never had
problems).
> 5) Can I write incrementally or do I have to write all at once?
>
This depends. There's something called "multisession support" that you would
need.
> 6) any other gotcha's or things I should know before I buy one?
>
The tricky thing about CD Burners is that they require a constant flow of data.
We purchased the YMI system because it has it's own internal disk cache. If you
are, for example, copying across the network and traffic heats up and you lose
data transmission for any period of time (second or two, possibly) then your CD
turns into a coaster.
Aside from the data archiving we do here, I personally like to use the system to
burn CDs with patch kits for Digital Unix and make "permanent" copies of user's
files before deleting their accounts.
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From: Bernd Scherer <bernd.scherer_at_vt.siemens.de>
> 1) What software do I need
We use software from am German Company called Point Software. You can have a
lookat here Webpage at www.pointsoft.de.
I attach the manpage for cdwrite which is the process for writing the CDs. This
will give
you an insight in the possibilities of this application.
> 2) which CD-R recorders are good for DEC's (or does it matter?)
We use the Yamaha CDR400 Recorder. You can get more Information
on
www.octave.com/cdrecorders/cdr400.html
> 3) are there features the drive needs to have in order to write Unix
> directories? (format, etc?)
It should support the ISO9660, so you can read the CD-ROM also an PC.
>
>
> 4) What do I need to do in order for the files be readable on Mac's and PC's.
ISO9660- and rrip-format
>
>
> 5) Can I write incrementally or do I have to write all at once?
With the Software and the CD-R you can write a Multisession-CD, which meansyou
don't have to write all at once.
> 6) any other gotcha's or things I should know before I buy one?
A good website for more Information is
www.cd-info.com
and there the page
www.cd-info.com/CDIC/Technology/CD-R/FAQ.html
Received on Thu Apr 23 1998 - 21:12:58 NZST