[Info-vax] Backup TK50 tapes

[glen herrmannsfeldt]

Johnny Billquist <bqt at softjar.se> wrote:
> On 2013-02-25 01:00, ChrisQ wrote:

(snip)
>> Funny how the rest of the world thinks that unix / linux gets it
>> right. Variable size tape blocks, who would have thought of
>> such a thing ?. Face it, VMS is now the odd man out now, irrespective
>> of how fine a system it is. Connectivity and portability are everything
>> these days. The network really is the computer..
 
> Well, the bottom fact is that every tape drive, even today, do variable 
> size blocks. It's the hardware. Now, if you have a OS that can't deal 
> with the actual hardware, you have a problem. No matter how fancy you 
> think you are.

Well, not every drive. There are some that are based on fixed sized
blocks, especially those based on a floppy disk controller. But a large
fraction of them do. 

Though some that have the ability to use variable sized blocks have
an option to do fixed size blocks. I once bought an Ultrium 1 drive
on eBay for a low price. It seemed to write, but the data didn't
come back right. I was writing 100K byte blocks, and 100 1K blocks
would come back. Turns out that the drive was in fixed 1K blocks mode.

(I believe in this case the blocking is virtual, such that there is
not inter-block gap cost for writing them. On older style drives an
actual gap is written, and data storage space is reduced.)

Also, the disk drives used with IBM mainframes can write variable
sized blocks. In the days of small memory computers, that helped
a lot. The ability to write larger blocks allows for more efficient
disk access.

(snip)

-- glen