Hi,
Greg Wooledge wrote:
> > > Remember, tar was designed for magnetic tapes,
> > > which are read sequentially. It provides no way for a reader to learn
> > > that file xyz is at byte offset 31337 and that it should skip ahead to
> > > that point if it only wants that one file.
rhkra...@gmail.com wrote:
> > Just to confirm, I assume that is true ("no way to skip ahead to byte
> > 31337") even if the underlying media is a (somewhat random access) disk
> > instead of (serial access) tape?
It is about not knowing to what byte address to skip.
tar is simply a sequence of file containers. File header, data, next file
header, data, and so on.
Lacking is a kind of directory, which predicts where a particular file
begins.
There are archivers which have such a catalog. With some quillings this
constitutes a filesystem.
> > In other words, I suspect it would be more reliable if it functioned a
> > little bit more like a WORM (Write Once, Read Many) type device
That would be CD-R, DVD-R, DVD+R, and BD-R media.
> > data is appended by writing in previously unused locations
> > rather than deleting some data,
That's called multi-session. It has other advantages beyond reducing the wear
of media. Typical filesystem for multi-session on write-once media is ISO 9660.
Greg Wooledge wrote:
> "Write Once, Read Many" is an entirely different data storage paradigm.
> Think of a large dusty vault full of optical media.
One can destroy them physically. Put stack-wise into the oven at 200 C / 400 F
for 10 minutes. Wear robust gloves when bending and breaking the hot media.
Single media can be destroyed by help of a lighter.
> Very expensive, and very niche.
One can buy 25 GB BD-R for less than a dollar, 50 GB for less than 2 dollar.
The usefulness depends on the storage constraints of orginal and backup.
> You can't reuse the medium, nor do you WANT to
If you want to re-use, there are CD-RW, DVD-RW, DVD+R, DVD-RAM, BD-RE.
Multi-session is possible on them with ISO 9660 filesystems.
Have a nice day :)
Thomas
