> Old stories, old news.  A CD-RW drive looks like any other disk
drive,
> except much slower.

Actually, at 16x write, it's about 2.4MB a minute, which is faster
than the 8MM tape drive.

And if you compress the data at about 6 to 1 using zip-style
compression, you get about 14MB a second, wich is as fast as
thefast mag tape drives are going (on actualy throughput). Not to
mention that you get about 4 GB of AS/400 data (uncompressed) on a
25 cent CD-R (which is what I would use rather than CD-RW).  So
for about $1.50 a day, you could have PERMANET backup of your
AS/400. Mutiple copies for $3.00 a day. That's very cheap
insurance.

My compression statistic are based on rather limited data. We saw
3X compression on a 2.74 MB library of RPG and CL source and
objects. We say 16X compression (94%) on spool files converted to
databases and backed up thru savlib.

6X may be a rather low estimate. I'm trying to be conservative.
\
And now 24X drives are out. I bought a 16X SONY CD-R/RW writer and
put it in my home PC last week- $99. I wrote a backup copy of my
favorite XMAS CD , the Narada Nutcracker in about 3 minutes. 24X
drives are now about $150.

> > Yes it is cheaper, but how does its reliability &
infrastructure compare?
>
> Your mileage may vary.  I guess it depends on whether you
consider a CD-RW a
> decent backup medium.  The fact that CDs cost about a buck and a
half apiece
> (for 700MB, or about 2 bucks a gig)

Again, if you get 6X compressin thats about 30 cents a Gigabyte.
On CD-R, it's about 6 cents a gigabyte. Fro most people it will be
cheaper, given the reliable re-use lifetimes of magnetic tape, to
back up permanently on CD. If you factor in the risk factor of
accidental reuse of the tapes, or the tape going bad between
backups, CD is hundreds of times cheaper.

For example. we develop software on PCs (much of which supports
AS/400 functions). Every Friday I get a neww CD-R that has all of
our program code, backup copies of our development tools and
libraries. I've got 50 of these offsite. Do I feel more secure
than if I had a daily magtape backup, reusing tapes in a cylce?
You bet your sweet bippy I do.

>  makes it pretty easy to cost justify
> double or triple backups;

It's not just the cost, it's the practicality. If you get 6X
compression, you can therefore make a copy of 4 GB of AS/400 data
in under 3 minutes with a 24X drive. 40 GB in 30 minutes or so
(assuming two drives and an attentive operator, or a robot CD
writer).

>  it's a lot harder to do that for tapes (e.g.,
> QIC-150, $18 for 150MB or around $125 a gig).  So, if you like
two backups
> (one onsite, one offsite), and you want redundancy in both
places, then I
> think you might want to seriously consider CD-RW.

And CD-R/RW drives are now out (I just saw one for $300) . They
write slower, but with compression you can get about 25 GB (of
AS/400 data) on one CD-R or RW. The media is still expensive,
about $7.50. But we know that will change.  And the drives will
speed up soon, I expect.

All of this presumes that you do a two stage backup - SAVLIB to a
PC with raided hard drives, then compress and write CD/DVD media
while the AS/400 goes on it's merry way. Reading and decompression
is much faster, so you can read from the CD, decompress, and drive
the tape interface at full speed. Not to mention the nearly zero
seeks time of random access CD versus serial access tape.

Brad Jensen




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