[rescue] Re: Re: Quick EXB-210 questions

[Greg A. Woods]

[ On Sunday, August 26, 2001 at 00:53:25 (-0700), Robert Novak wrote: ]
> Subject: [rescue] Re: Re: Quick EXB-210 questions
>
> They're for backing up my home network, for when I need to migrate a
> system or replace a failed hard drive. I have found 8mm metal particle to
> be quite sufficient for this so far. Admittedly this might be in line with
> published reports, but I've found that very little that I've done is
> impossible.

then like me you don't have to worry so much about designed-for duty
cycles, etc.

> Well, you can't say that anymore. I've had real experience with really
> needing my backups when the proverbial smelly stuff hits the fan big-time,
> on 8mm media, and no fasteners of any sort even began to speculate about
> the merest possibility of crossing my lips. 

Either you were lucky (that happens), or the smelly stuff wasn't really
sticky and didn't trigger enough to trigger Finagle's law of dynamic
negatives!

Sure I've restored with 8mm, and even 4mm, after a drive dies, or some
such simple problem, but I've not had to rebuild a system from off-site
backups after the building burned down (at least not since QIC-150 was a
new thing!).

> What do you use for your home backups, by the way? SDLT? 9-track? 

Like I already said, an EXB-210 with an Eliant-820 in it.

But the truth be told I've not been able to do a backup for months
because the NetBSD siop driver does not work (for tape drives) and the
ncr driver has been removed from the tree (because it would need a *lot*
of work to re-integrate into the scsipi architecture).  So all I really
have for my backups are the two spare drives in my three RAID arrays,
and that only covers /home, /cvs, and /work (whis is, luckily, where
everything really important resides).

> I have trouble believing any report that has no downsides, but maybe you
> haven't run into the downside yet.

The biggest downsides to DLT are costs:  media and drives are expensive.

DLT drives are usually a bit larger and usually require more power too.

DLT media requires somewhat more careful handling, though if your
backups are important to you that difference is kinda moot.  The extra
strengh of having 0.5-inch wide tape usually makes up for the difference.

> Or maybe DLT is actually perfect except
> for noise and slow access time and increased pass count.

I think you have that at least partly WRONG there!

DLT media will survive at least an order of magnitued more passes than
anything helical-scanned.  While the speed of the head passing by the
tape is more or less the same on all the competing drives, the
difference with DLT is the simplicity of the tape path and the fact that
the recorded side of the tape never touches any mechanism but the head
itself.  Most independent studies suggest it'll last for at least one
million passes while helical scan 8mm is only good for about 20k or so.

(of course you don't want more tape life with AIT-2 since the silly MIC
chip in the cassette will die before then anyway!)

Only Tandberg MLR can compete in tape life with DLT and exceed it in
drive life, and that's because it's essentially the same technology as
DLT but with an enclosed dual-spool cartridge like QIC where all but one
of the moving parts are in the cartridge.

DLT's aren't really that slow, and can have much better random access
than most forms of helical-scan devices, equalled only by AIT.

DLT gains its access speed with a file mark index recorded at the
beginning of the tape and it can find files without reading all the
intervening data.

> Or maybe it
> really has been around longer than CD technology... I know I have CDs that
> are 15 years old and still work. How many DLT tapes do you have that are
> that old and still read without errors?

I have CDs that are less than 15 years old and I can see light through
pinholes in them.  They might not make it to 15, even for just audio
playback.

Chemistry and physics are not on the side of CD, CDR, and CD-RW.  They
are already proven to last for less time than old-fashioned 9-track
magnetic tape (which if stored right might last 100 years).

Longevity for me means keeping *all* of my data on-line on secondary
storage -- backups are just to bridge failures of the on-line devices.

> But anyway, this is starting to smell like a religious debate. I'll go

A couple of independent study reports:

	http://www.str8line.com/products/downloads/tapetechcomp99.pdf

	http://www.pctechguide.com/15tape2.htm

The corporate line:

	http://www.digitalstorage.com/enduser/product_info/Specs_FAQs/quantum/dlttape_handbook.pdf

> back to working on my P2B-S system (yeah, I know, if you had a penny for
> every Intel architecture motherboard that spontaneously combusted and
> destroyed civilization as we know it...)

hmmmm..... now what could I do with such riches?  :-)

Unfortuantely almost all of my critical home office infrastructure now
runs on i386, though all of it on "real servers", not desktops! -- only
the superfluous stuff runs on sparc (and the old pdp11's, 3b2's, sun3's,
vax's, decstations, multias, etc. are all sitting quietly hibernating).

-- 
							Greg A. Woods

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