Re: FIFO

Hi Joerg,

Joerg Schilling wrote:
> "Zoran Ljubisic" <[email protected]> wrote:
>
> If Linux honores this, you will most likely end up in usually
> unreadable tapes.

I think I don't understand your sentence here. Can you be more accurate 
please?
Why should I end up in usually unreadable tape?

> It may be however that Linux does not honor
> blocking at all :-(
> If sdd if=/dev/tape bs=10m -onull -deb ug does not show you the 8MB
> Blocks, Linus did give you 512 byte blocksize.

SuSE 9.3 prof don't have on it's DVD "sdd" program.
Can I use dd instead?

> For best tape interchange never use bs > 63k because there are a lot
> of DMA controllers that cannot support >= 64k.

I need tapes to be available only on one machine so bs > 63 should be OK.

> For best tape interchange in recent OS never use bs > 126k.

What bs than you will suggest to me if you know that I am running SuSE 9.3 
prof with HP StorageWorks 72i (36 GB native 72 GB with hardware 
compression)?

>> I noticed that tape LED sometimes stops blinking for few seconds
>> than starts blinking again.
>> Do I have problem with FIFO?
>
> No, but you may have a problem with the I/O speed of you OS.

Is there any help about it?

> But note that even HP does only advertize a (compressed) Transferrate
> of
> 6.5 MB/s at max to the tape drive, so what is your point?

I am expecting that FIFO held enough data to serve for tape drive so LED 
never stops blinking until backup is finished.

> If you get less that 2:1 compression, you transfer rate will go down.

My files are mostly *.dbf FoxPro for DOS tables and word or excel documents.
I think for dbfs compression should be much more than 2:1 and for word or 
excle document must be at lease 2:1.

> If you like high speed and high quality, never use a DAT tape drive.

You are probablly right, Joerg.

Zoran