HELP: scsi tape and tape block size - how to user control

HELP: scsi tape and tape block size - how to user control

Post by Jason Venn » Sat, 08 Apr 1995 04:00:00



In v1.X, I always patched drivers/scsi/st.c so that it did not do buffered IO,
so as to be able to control the tape block size. This is necessary for me as I
have to be able to import and export tapes at various blocking factors.

the 1.2.X st.c is very different and my first guess at the patches
failed miserably.

What is the way to turn on user controlled read/write block sizes for
scsi tape drives?

I use a WangDat 6200-HS.

Thanks -- Jason

 
 
 

HELP: scsi tape and tape block size - how to user control

Post by stev » Wed, 12 Apr 1995 04:00:00




> In v1.X, I always patched drivers/scsi/st.c so that it did not do buffered IO,
> so as to be able to control the tape block size. This is necessary for me as I
> have to be able to import and export tapes at various blocking factors.

> the 1.2.X st.c is very different and my first guess at the patches
> failed miserably.

> What is the way to turn on user controlled read/write block sizes for
> scsi tape drives?

> I use a WangDat 6200-HS.

> Thanks -- Jason

Hi,

Why can't you use mt?? I use mt all the time to set a zero block size
i.e.

   mt -f /dev/rmt0 setblk 0

Always seems to work for me when reading DAT tapes from non-Linux machines.

Cheers,
Steve.

 
 
 

HELP: scsi tape and tape block size - how to user control

Post by Joe Bu » Wed, 12 Apr 1995 04:00:00



>In v1.X, I always patched drivers/scsi/st.c so that it did not do buffered IO,
>so as to be able to control the tape block size. This is necessary for me as I
>have to be able to import and export tapes at various blocking factors.

Why go to all this work?  Doesn't the "dd" program work for you?

--

Phone: +1 415 694 1729

 
 
 

HELP: scsi tape and tape block size - how to user control

Post by A.Nar » Wed, 26 Apr 1995 04:00:00



: >In v1.X, I always patched drivers/scsi/st.c so that it did not do buffered IO,
: >so as to be able to control the tape block size. This is necessary for me as I
: >have to be able to import and export tapes at various blocking factors.

: Why go to all this work?  Doesn't the "dd" program work for you?

SCSI Tape Drives can have there own Hardware blocking factor as well as
a software controlled one. Streaming tape drives do not do this, and only
look at the software blocking factor.  

I can see where this guy can run into problems.

I've seen how various other Unix's have handled this. Some use different
SCSI Tape device names while others can control this setup directly.

There is even a modified version of gnu tar floating around that has the
added option "physrecsz" that controls this.                      

The blocking factor that software apps use (dd, tar, etc) generally do not
refer to hardware blocking.

Just letting you know.                    

-Alan

 
 
 

1. Appropriate size of dump tape blocks for high density tape

A tape block is 1024 bytes. Dump writes blocks that are multiples of this
size. The default blocking factor for 1600 bpi tape is 20. That means that
each block written to the tape is 20*1024 bytes.

Now on to tapes with higher density. I have a cartridge tape and have
been recommended to use a blocking factor of 126. I have perused the kernel
with adb and verified that the driver calls
        minphys()
It is my understanding that minphys will ensure that blocks larger than 63
kbytes are split up so that no entity larger than 63 kBytes are written.

Would a blocking factor of 63 be more correct (yes, I notice that 63*2 = 126,
so no great harm is done).

Assuming that you have a fast tape drive, is it more efficient to write
blocks that are an even multiple of the size of a disk block?

--
Johan Widen
SICS, PO Box 1263, S-163 13 SPANGA, SWEDEN
{mcvax,munnari,cernvax,diku,inria,prlb2,penet,ukc,unido}!enea!sics.se!jw

2. LILO prompt

3. SCSI tape gives 'wrong block size'

4. PPPD 2.3.1 & Linux Kernel 2.0.30-3

5. Trying to determine scsi tape density/block size/length for dump

6. Potentially HORRID news for Linux and the Web

7. TAR problem from SCSI Tape: Wrong Block Size?

8. FDISK megabyte calculation ?????

9. Block Size of SCSI DDS-2 Tape Drive

10. SCSI tape block size

11. Finding the block size of a file on tape - block.c (0/1)

12. need help with tar and default tape block size

13. ADAPTEC 1542B DOES NOT RECOGNIZE SCSI TAPE DRIVE AND SCSI TAPE ?