[rescue] Backups

[Jeffrey Nonken]

On Thu, 16 Jun 2005 13:44:09 -0400, velociraptor wrote:
> On 6/16/05, Jeffrey Nonken <jjn_rescue at nonken.net> wrote:
>
>> OK, good to know. I'm still not sold on DLT but I'll take a look.
>>
> Just a point of data: All linear tape solutions (DLT, AIT, LTO) are

Um, AIT is 8mm helical scan. (A format which has never, ever given me
a single problem, I might add. And the drives are self-cleaning and
100% duty cycle. :)

QIC/Travan is also linear.
>
> The most important consideration for maximum tape writing
> efficiency and longevity with linear tapes/drives is the data
> stream to the tape drive.  If there is not sufficient data being
> fed to the drive, the tape will "see-saw" over the tape head
> wearing both the tape and the tape head.
>
> The tape see-saws because data is written in bands onto the tape,
> e.g. a hypothetical block looks like:
>
> ===
> ===
>
As I understand it, the tape see-saws ("shoe polish") because the data
are streamed and it has to splice the data on the tape. (It has to
back up and get a running start so it's moving at recording speed when
it reaches the end of the data.) One of the advantages of helical scan
is that the medium is moving more slowly so it takes less time to
reverse, and causes less wear on the drive.

Unless you're talking about the fact that it (the linear methods I'm
familiar with, that is) records to one end, then records to the other
on alternate tracks (serpentine method), in which case I misunderstood
what you were trying to say.

>
> I suspect IDE will likely not be fast enough to feed the beast
> unless you stream multiple jobs across the net- work.
>
I don't know about LTO. AFAIK most if not all AIT and DLT drives are
wide SCSI, and DDS are various widths of SCSI.

I'm not that concerned about the interface method as such. I have wide
and narrow SCSI controllers, and I believe my wide controller supports
SE and LVD. I should be covered.

Obviously if I want maximum performance I want to use something with
wide differential SCSI.