> The first is the size issue.  Note the discrepancy between DL-IV media
> vs. the lowest cost/GB ATA drives.  There are several implications and
> alternatives here.  Obviously the first issue is that you've practically
> (though not strictly) got to keep your filesystems down below 40 GB if
> you go with DLT IV for backups.

Not so.  I regularly back up filesystems that are hundreds of gigabytes in
size.  You simply need to use backup software that can have backup objects
span multiple tapes, which is commonplace.

You can also find higher capacity tapes, like LTO.

> However the big kicker is the price of the [S]DLT tape drive.  Yes you
> only buy one of those (until it fails), however they're still very
> expensive, especially compared to the infrastructure necessary to
> support ATA drives.

The price difference is less noticable when you buy hard drives that will
last longer than a year, and enclosures to house them in.

> Perhaps even more important is the fact that ATA drives are still
> keeping well ahead of tape media in raw capacity per unit and in
> transfer speeds.  Think about the relative transfer rates of having one
> DLT or SDLT drive in a tape library vs. having three or four
> simultanously (and much faster) writing ATA drives.  Even if you do
> decide to allow your backup data to be compressed and thus have to burn
> a wee bit of CPU to make up for the compression normally done by the
> [S]DLT drive, you still don't have to pay any more (assuming any even
> half-modern CPU and especially not if you only do the same 2:1
> compression a drive can do).

LTO2 provides 20MB/second native, which is about the write speed you get in
the real world from ATA133.

> Now think about this just a wee bit harder:  we're equating ATA random
> access high-speed disk drives with tape media!  Think of the
> implications!

Typically when you are restoring data, you restore a chunk, for example a
whole filesystem or directory tree.  It is common for backup software to be
able to seek to a spot on the tape, and restore the data very quickly.

Ben