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Re: DLT IV takes longer than DLT III

 
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Robert Milne
Frequent Advisor

DLT IV takes longer than DLT III

Hi All,

I have a dilemma, when running our midday backup using the usual DLT III tapes backup duration is approx 3-3.5 hours in length.

I recently had to swap out a faulty tape for a new HP DLT IV Tape, when using this tape for the EXACT same scheduled backup, during time is significantly increased..
Backup length increases to 5 Hours..

Can anyone explain why this is the case?

My Server, Tape Drive, and Backup Type are below.

HPUX 9000 L1000

HP 8000 DLT Tape Drive

Simple TAR backup

Cheers

Chris
"For every pleasure there's a tax."
12 REPLIES 12
Shaikh Imran
Honored Contributor

Re: DLT IV takes longer than DLT III

Hi,
Lot of questions still..
What is DLT III & DLT IV ?
Is DLT 8000 your current drive ?
What was your earlier drive ?
Assuming that DLT 8000 is the current drive:
Do you have the right media for the right drive ?
I have faced only 2 reasons for DLT 8000 running slow
a) firmware version
b) The head-gear assembly in the drive which i got replaced once successfully.

The second reason (b) is as good as replacing the drive.

Also i will advise you to download LTT and have other check for the drive.
Follow the link:
http://h18006.www1.hp.com/products/storageworks/ltt/specifications.html
download the LTT as per your O.S.
and carry on the test.


Regards,




I'll sleep when i am dead.
Robert Milne
Frequent Advisor

Re: DLT IV takes longer than DLT III

Sorry..

DLT III and DLT IV are types of DLT Tapes.

I.E. DLT 3 15/30GB and DLT 4 40/80GB

Can hold different capacitys...

I dont think there is anything wrong with the tape drive, (HP8000) as it was recently replaced after a failure.


Chris

"For every pleasure there's a tax."
Shaikh Imran
Honored Contributor

Re: DLT IV takes longer than DLT III

Hi,
Please check for the SCSI termination.
If possible reseat the terminator.
If you doubt O.S. then pls use other command e.g. cpio and try to get the speed.

BTW,Have you got a fresh brand new DLT drive or it's a replacement (used one). ?
Either case this seems to be a problem with the drive which can only be tested by replacing and testing it.

Regards,

I'll sleep when i am dead.
Robert Milne
Frequent Advisor

Re: DLT IV takes longer than DLT III

Once again, I dont believe this problem is caused by a faulty DLT drive.

If it were then i would be getting variable backup times everyday..

This is not the case, If i use a DLT III Tape then the backup takes 3 hours, if i use DLT IV then backup takes 5 hours.

The Tape Drive is NEW, and is not defective.

Chris
"For every pleasure there's a tax."
Ashwani Kashyap
Honored Contributor

Re: DLT IV takes longer than DLT III

I think it might be formating related issue . Have you tried to initialize the DLTIV media on your current drive before taking a backup .
Robert Milne
Frequent Advisor

Re: DLT IV takes longer than DLT III

Can you please explain how I can do this?

initialising??

Do you mean a mt stat??

Chris
"For every pleasure there's a tax."
Mark Carlson
New Member

Re: DLT IV takes longer than DLT III

Chris,

The DLT-III tape media and DLT-IV tape media are physically different inside the cartridge. DLT-IV has 50% more tape in it which may account for the 50% increase in backup time.

Typically the drive accounts for increased density as part of normal operation. I'm no drive expert but assume there is may be a setup function that would allow maximum speed operation.

Alternately you may be running into a situation where the DLT8000 running with DLT-IV media is outpacing the ability of the your host to stream data. This interesting condition could actually result in a decrease in throughput.

Should be plenty of drive experts out there with experience in your combination/situation...
Scott McIntosh_2
Honored Contributor

Re: DLT IV takes longer than DLT III

DLT 8000 tape drive
with DLTtape IIIXT - 1.5MB/s & 15GB
with DLTtape IV - 6MB/s & 40GB

So the streaming concern is valid. But I'm not sure that it would account for running at less than 25% native rate.

3-3.5 hours at 1.5MB/s is 16GB or so, basically one full tape. Are you sure your backup is taking 3-3.5 hours, or filling up a tape is taking 3-3.5 hours? If the backup, then you're likely not even getting a 1.5MB/s data rate out of tape drive front end (buffer and compression). Which would only become a worse problem with the higher speed DLTtape IV would be wound at.

Thanks,
Scott
HP Support
Robert Milne
Frequent Advisor

Re: DLT IV takes longer than DLT III

The backup consists of the backup of files, then a tape readback of contents..

So i imagine that actual writing to the DLT III tape takes only 1.5 hours, and then the read back for the remaining time?

Would i be correct?

Chris
"For every pleasure there's a tax."