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Hello Gad,

Am 03.08.2022 um 09:37 schrieb Gad Miron <gadmiron@xxxxxxxxx>:

I'm trying to speed up a nightly save to a 3580 LTO7 stand alone tape drive
and would like some advice with the following:

a. Will specifying COMPACT(*NO) on the SAVLIB CMD expedite matters ?
we now use DTACPR(*DEV) and COMPACT(*DEV)

I'd leave it at this default. The tape drive is allowed to compress data in hardware. Thus, data might flow in faster into the drive logic than needs/can to be written to tape. Additionally, more data fits on tape.

About speed: My limited experience with mostly older machinery (newest is a p6 with a LTO4 drive) proved that backups on OS/400 and successors are never really fast — compared to common systems. I guess this is because all data has to go through paging into RAM and then to tape instead of reading a stream of bytes directly from disk into RAM and to the tape drive, but I might be wrong. Doing backups of many small files on common systems also is much slower than writing one huge file.

Sometimes, the (lack of) speed needs rethinking the overall backup strategy.

b. On a 3580 spec web page I found a remark pertaining to Full Hight vs.
Half Hight
models . see remark No.7 on this page

Is a Full Hight model Faster the Half Hight? or Vice versa?

It is *said* that Full-Height (to be precise: Double-Height) drives are faster than smaller ones. In a way, this makes sense: The motor coils are better separated/shielded from the tape cartridge itself. There is less chance to destroy data, so the coils might be driven "more aggressively" to make the tape go back and forth quicker. Also, more space means better airflow for cooling the electronics and coils.

I have not yet done precise measurements, but this is on my list to try out with LTO1 drives I have spare.

:wq! PoC

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