Re: FIFO

"Zoran Ljubisic" <[email protected]> wrote:

> Hi,
>
> Look in this (-fifostats -time):
>
> star: fifo had 438235 puts 591 gets.
> star: fifo was 22 times empty and 35 times full.
> star: fifo held 125829120 bytes max, size was 134217728 bytes
> star: 591 blocks + 0 bytes (total of 4957667328 bytes = 4841472.00k).
> star: Total time 983.759sec (4921 kBytes/sec)
>
>
>
> Is it normal for fifo to be 22 times empty and 35 times full?
> My comp is SuSE 9.3 prof on Athlon 64 3000+ with 1GB RAM on soft RAID 1 
> (mirroring) 2 disks + HP tape drive StorageWorks 72i DAT ( C7438A 
> http://h18006.www1.hp.com/products/storageworks/dat72/index.html attached to 
> http://www.koutech.com/proddetail.asp?linenumber=136 scsi controller). My 
> DAT have 8MB buffer so I am using bs=8m.

If Linux honores this, you will most likely end up in usually unreadable
tapes. 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.

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

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

> 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.

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

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



Jörg

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