tar, Linux, and DAT drives questions

[Scott Horton]

These questions based on following inst on

http://www.hp.com/cposupport/information_storage/support_doc/lpg51060.html

Thanks very much for the previous answers about my older DDS-1 drive. I have the unit working (sort of). I have 2 more HP DDS-2 drives on the way I liked this one so much .

If I issued a
mt -f /dev/st0 retension
I got errors but since I'm told DAT does not need retensioning, that was probably why.

If I do:
mt -f /dev/st0 rewind
it takes it, and I assume it rewinds, this is good.

But I tried setting the dips to have host control of compression , and then issued:
mt -f /dev/st0 compression
(inst. said to use "datacompression" but that's not an option with my mt)
but I get
Input/Output Error
when trying that. I guess I'll set the dip's to force compression unless someone has a suggestion.

Finally, I followed another example on this form to use tar to back up and restore some files. The command included an argument for block size of 20. When I issue the tar command with that argument, it chokes but works OK without it. What block size should I use with this drive, and where/how would one set it's default? HP's tech docs say if it's on UNIX, see you system administrator, but that's me and I haven't got a clue how to set/change the block size. Again, & FWIW, I'm running Linux kernel 2.4.5 with a Buslogic SCSI card.


Thanks very much for your time to help me.

Scott
Nashville, TN

P.S. This thread has been moved from General to Linux > sysadmin. - Hp Forum Moderator

[Eric de Lange_2]

Hello Scott,

The correct syntax to enable compression with mt is: 'mt -f /dev/st0 datcompression on'

Tar and cpio by default use 512byte blocks. With older and slower tapedevices like DDS1 that is not too much of a problem. With faster tape devices this gets more important especially with the Ultriums that pump away 30MB/sec.

I'd use the 'b' option in tar that gives a blocksize of 5120bytes. ('B' in cpio I think)

If you don't like all this commandline violence for a little backup, there are plenty of nice GUI's that give you a graphical environment on top of these commands. Some are free, some are commercial, check it all out at http://www.linux.org/apps/all/Administration/Backup.html.

best regards,

-Cal.

[Scott Horton]

>The correct syntax to enable compression with >mt is: 'mt -f /dev/st0 datcompression on'

As I mentioned in the orignal post, "datacompression" is not a valid option with my "mt". I am using RH Linux 7.1, mt ver is:
mt-st v. 0.5b

Tar and cpio by default use 512byte blocks. With older and slower tapedevices like DDS1 that is not too much of a problem. With faster tape devices this gets more important especially with the Ultriums that pump away 30MB/sec.

>I'd use the 'b' option in tar that gives a >blocksize of 5120bytes. ('B' in cpio I think)

My tar b option is how many x 512, default of 20. You are recommending 5,120? Seems high compared to the default.

Question is what is the best block size (quantity) for a DDS1 and as long as I'm asking DDS-2 drive?

>plenty of nice GUI's that give you a >graphical environment on top of these >commands. Some are free, some are commercial,

Thanks for the links. But I'm old school, don't even use X on these boxes and still like the command line.

Cheers,
Scott

[Eric de Lange_2]

As I mentioned in the orignal post, "datacompression" is not a valid option with my "mt". I am using RH Linux 7.1, mt ver is:
mt-st v. 0.5b

>> I am running 7.1. I just tested the 'datcompression on' option succesfully. You are typing 'datacompression' which is not an option.


My tar b option is how many x 512, default of 20. You are recommending 5,120? Seems high compared to the default.
>> It is not too high. Most backup applications have a default of 16k or 32k. Omniback even defaults to 56k or 64k with an option to go even higher.

>> With DDS1 you are reasonably safe but with higher performing drives using this blocksize will eventually kill the drive prematurely.

Thanks for the links. But I'm old school, don't even use X on these boxes and still like the command line.
>> point taken.

Have a nice weekend.

-Cal.

[Scott Horton]

Cal:

I'm embarrassed to see my typo using "data" instead of "dat" as in datcompression. Thanks very much for helping me see it.

I'm still fuzzy on the block size. Let me try to phrase the question again to be sure I understand:


The parameter to send tar is how many 512k blocks. So do you mean,

DDS-1:
use 10 with tar so I get
10 x 512 = 5120

or do you mean:

use 5120 as the parameter so it would be
5120 x 512 = 2621440

Sorry to be so dense.

I also have a HP DDS-2, and I don't want to wear it out prematures, what block size shoudl I use with it?

Thanks again for the help and clarification!

Scott

[Eric de Lange_2 · Accepted solution]

The parameter to send tar is how many 512k blocks.
>> Actually, it is 512 bytes, not 512k

DDS-1: use 10 with tar so I get 10 x 512 = 5120
>> Yes, this is correct

I also have a HP DDS-2, and I don't want to wear it out prematures, what block size shoudl I use with it?
>> Depends on the sort of data you're backing up with the thing. I would definately go for 5k blocksize minimum.

The premature wear is caused when the drive is not allowed to write the data in one fluent, streaming motion but has to stop and wait for data to come from the host. All this stopping and starting is putting a lot of additional wear on the drive but also on your tapes. Something to be aware of....

Cheers,

Cal.