Gavin writes:

>John writes:
>> Well, I seem to remember the IRG as being 0.5 inch.
>>
>> Assuming the record size to be 16,384 bytes, at a tape density of 6250 bpi,
>> a record (16K bytes) takes up approximately 3.1214 inches of tape
>> (including the 0.5 inch IRG).
>
>Hence the ;MAXTAPEBUF option on :STORE that, I believe, causes it to
>create 32,768 byte records, cutting the IRG overhead in half.  Of course
>STORE has to bypass the file system to perform reads and writes this
>large, which limits the number of tools that can operate on such a
>tape on a 3000.

The 7980XC uses 65,536-byte blocks when operating in compression mode.
This cuts the number of IRGs in half again, even for uncompressible data.
The firmware on the drive unpacks these blocks into the user's original
blocks when the tape is read.

-- Bruce


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