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DLT IV TAPES - PERFORMANCE

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DLT IV TAPES - PERFORMANCE

I am currently running an HP 80e (DLT8000) ape drive on a Windows 2000 system with Arcserve 2000.

The issue I have is that the unit appears to get very fussy over individual tape batches.

Currently we have had to return 10 Maxell tapes all from the same batch because the unit speed droped from 330MB/min to 40MB/min over the length of the tape (normally after 500MB the rate starts dropping).

Now I know (or at least think) the unit is fine because we purchased 20 Maxell tapes at the same time and onlt 10 tapes exhibit the problem.

When the problem was first noticed it appeared to be random however after logging the issue closely it was noticed that this only happened on specific tapes, we then noticed from the stamp on the bottom of the tape that all those effected came from the same batch. Problem solved - well not quite.

I have now obtained some brand new HP tapes and once again the unit only likes certain tapes from those purchased. The other less fortunate tapes are snubbed by the system. Now I know HP tape warranty to cover tapes for 20 years but I'm sure they will claims that the tapes have no problem - except for the fact that my system will only backup at 330MB/min on the tapes it likes and anything else it will struggle at 90MB/min.

The question I have is there any benchmark utility out there that will chart the backup performance of a tape over its entire length.
HP Tape Tool is simply not sophisticated enough.

NB All tapes are brand new and only used on this unit. I am aware of the issues regarding DLT8000 and VS80.
13 REPLIES
Alexander M. Ermes
Honored Contributor

Re: DLT IV TAPES - PERFORMANCE

Hi Craig.
1) Try to download the ltt tools and test your environment.

2) what about the file sizes ? if the files are small, the tapedrive will not go into streaming mode ( repositioning after every file takes a lot of time ).

3) Do you work with software compression on ?
Try to switch it off, because the hardware compress is much more effective and does not work well together with software compress.

I hope, that this helps.
Rgds
Alexander M. Ermes
.. and all these memories are going to vanish like tears in the rain! final words from Rutger Hauer in "Blade Runner"
Alexander M. Ermes
Honored Contributor

Re: DLT IV TAPES - PERFORMANCE

Hi Craig.
Here the URL for the ltt tools :

http://h20000.www2.hp.com/bizsupport/TechSupport/DriverDownload.jsp?pnameOID=406731&locale=en_US&taskId=135&prodSeriesId=406729&prodTypeId=12169

Rgds
Alexander M. Ermes
.. and all these memories are going to vanish like tears in the rain! final words from Rutger Hauer in "Blade Runner"

Re: DLT IV TAPES - PERFORMANCE

LTT tools are useless for the problem described above. They are far to blunt.

I have run LTT diagnostics against the system the drive is upto date and a cant see anything that stands out.

The file sizes are mixed and as described above I have a dedicated TESTJOB that backups up a specific VOLUME full of various sized files.

Tapes that the system like complete the backup in approx 3mins at an av rate of 330MB/min.

Tapes that the system does not like complete the backup anything upto 20mins with av. rates as low as 50MB/min.

The above is repeatable and I can predict the results for tapes run through the test once (they always behave the same no matter what time of day or what else is being run on the system). All the tapes being tested currently are brand new shrink wrapped tapes.

From observation the tapes that do not perform well all appear to start well at 330MB/min but by about 50% through the job (some 600MB into the job) the backup rate starts to drop. Yes compression is switched on. In order to isolate the problem further I may change the directory to contain a commonly available file such as the Microsoft Service Packs. These should be sufficent in size to allow the drive to max out (however in the test above I would concider an average of 300MB/min and above max speed.

As the original post what I am looking for in an application the will produce data rates across the entire tape lenght so I can produce a graph to show DataRate vs TapePosition. The perfect graph should show a straight line. From the observation above the graph slides down for the 'unliked' tapes. The alternative is to sit and document throughput rates by hand during the testjob!

The only explination I can think of at the moment is the the drive starts to lose the tracking track on the tape. Maybe the drive is drifting from true alignment which means marginal tapes are effected as above whilst very good tapes are okay.

My only option is to return tapes as faulty to the manufacturer as the system above demonstrates that the results are repeatable and that tapes of the same brand are accepted without problems.

PS Just for the record I have used LTT to do Write and Verfy tests to the tape however these test are limited to 2GB data sizes maximum and the results are not consistent.

Re: DLT IV TAPES - PERFORMANCE

One thing I do need to check is the block size currently selected via Arcserve however this still does not explain why some tapes are fine straight out the wrappers whilst others are useless.

I guess ultimately it could be as simple as the handling and storage whilst in the sales channel!

This could have explained the first variance however using different suppliers and brands the same is true. Or maybe for the first time I am scrutinising every new tape before it goes into production.

[Never had these problems with DAT or SLR]

Re: DLT IV TAPES - PERFORMANCE

PS Just for the record I have used LTT to do Write and Verfy tests to the tape however these test are limited to 2GB data sizes maximum and the results are not consistent.

The above comment related to the fact that all you get in the results is passed and a time for the test section. These are meaning less as it does not give any indication of data rate across the media (only and average if you use some maths).
David Ruska
Honored Contributor

Re: DLT IV TAPES - PERFORMANCE

Craig,

If you can run the backup that is slow on an individual tape, and then run HP LTT and generate a support ticket WHILE THE TAPE IS LOADED, I can look at the read/write error counters and see what type of error rate you are getting. If performance of one data set varies dramatically between tapes (and consistantly), usually it's an error rate issue. The device analysis section of the support ticket may also print out the number of corrected errors.

The reason you need to do this while the tape is loaded is due to the DLT drive clearing its error rate counters as soon as the tape is unloaded.

Also, I'll mention that the DLT drive in particular does not like small block sizes and can easily fall out of streaming which slows things down considerably. You should use a block size of 64K or better.

HP Engineering
The journey IS the reward.

Re: DLT IV TAPES - PERFORMANCE

Hi David

Thanks for the offer. When I get into the office I will produce a support ticket (however last nights backup was on tapes known to be good) I will then run a complete job on a known poor tape tonight and upload that in the morning!

I will also grab the external drive and put it on another system for more analysis.

Since the above posts I have used LTT a little more and found that the product support upto 16GB tests (my error). However running these test even on the poor tapes produces aceptable results that are not shown in the real world under Arcserve.

Looking at the tape statistics under Arcserve I can see the block size on the tape is set to 65536

I would greatly appreciate your time to look at the ticket info when posted.

(I probally post a zip of some additional information and multiple tickets all clearly labeled as I could do a short job of say 1GB mixed data that shows the errors).
David Ruska
Honored Contributor

Re: DLT IV TAPES - PERFORMANCE

Craig, thanks for the additional information. You can email the support ticket and any other info you have to ltt_team@hp.com.
The journey IS the reward.

Re: DLT IV TAPES - PERFORMANCE

Hi Dave

Thanks. I have sent an email with a copy of the ticket produced today on a 'poor' tape.

I will email more information over the weeknd when I have had time to test on a different system.
David Ruska
Honored Contributor
Solution

Re: DLT IV TAPES - PERFORMANCE

Thanks for the logs. The DLT drive has a considerable number of cleaning and error rate related soft error messages. Here's some examples:

---
Event # 45 - Packet # 173 - SCSI Event: Cleaning required
Temp 37 C
POH/PC/MID/SK/ASC/ASCQ/AddErr=21242/35/78D71592/3/80/01/00
Event # 46 - Packet # 174 - SCSI Event: Cleaning requested
Temp 39 C
POH/PC/MID/SK/ASC/ASCQ/AddErr=21257/35/78D78703/1/80/02/00
Event # 47 - Packet # 175 - SCSI Event: Soft Error Exceeds Threshold
Temp 37 C
POH/PC/MID/SK/ASC/ASCQ/AddErr=21268/35/78D78703/1/80/03/00
---

These are within the last 100 hours (POH=Power-on-hours) of use.

The 20041001_tempjob_poortape.ltt file shows the following:

Drive Error Statistics
Read errors corrected w/substantial delays : 0
Total read rewrites or rereads : 0
Total read errors corrected : 0
Total read bytes processed : 0x0000000000119EA0
Total read uncorrected errors : 0
Write errors corrected w/substantial delays : 0
Total write rewrites or rereads : 4171
Total write errors corrected : 4171
Total write bytes processed : 0x00000000460EEA70
Total write uncorrected errors : 0

If you take the number of rewrites and divide by the total bytes (displayed in hex), you get a representitive error rate calculation. In this case it would be 4171/1175382640, which comes out to 3.5 rewrites per MB. That's poor error rate. Anything over 1 per MB will have a noticable hit on performance.

The other ticket, 20041001_Overnight.ltt, does not have error rate data. The drive status is "load command needed" which most likely means the host sent a command to unthread the tape (although the cartridge may still be in the drive).

The cause of poor error rate can be due to any of the following:
* Dirty head (normal staining & debris)
* Contaminated head (from environment)
* Worn/profiled head
* Electronics problems
* Worn media

If the head is stained from normal use, running a new cleaning tape through the drive 3 times in a row will typically clean it up.

Head contamination is harder to remove with a cleaning tape, although sometimes it helps. Some sources of contamination we've seen include in the past include smoke, soot/ash, paper dust (from printers), ink (from inkjet printers), carpet fibres, and outside dust.

Over time the tape drive head wears, since it is in direct contact with the media. It's therefore possible for the head to profile as a result, and that may make it read/write on one manufacturers formulation better than another. The tape stiffness and abrasitivity can vary within the allowable range from vendor to vendor.

The tape serial numbers you included in your email indicates that you have tape from two different manufacturers. There's a letter in the middle of the SN that indicates which one. You can see if your test results show one working better than the other.

Since you mention having problems with new tapes, we can rule out worn tapes as the cause. Note that new media may occasionally have higher error rate for the first few passes down the tape, as there is some debris that gets left by the splitting process, which typically cleans itself off with a fairly short amount of use.

If you conclude the head is worn, then the only real solution might be to replace it.
The journey IS the reward.

Re: DLT IV TAPES - PERFORMANCE

Thank for looking at the log files. Thats a lot of information you've gathered.

I will try cleaning the tape drive as you suggested. Then I will run LTT tape test on the two different sets of HP media and save the log files.

If you would be willing to look at these two files and give me a final analysis, I would appreciate it.

Thanks you for your time so far in helping me.
David Ruska
Honored Contributor

Re: DLT IV TAPES - PERFORMANCE

Craig,

No problem. Just send them to ltt_team again, and post a quick reply here so I know to go look for them.
The journey IS the reward.

Re: DLT IV TAPES - PERFORMANCE

Hi Dave

I have posted up the LTT support tickets. If your able to give me some advice based on your experience on the units that would be great.

With regards to the back up jobs the data rate has improved to 295MB/min average (not too far from the 315MB/min target).

At the moment I'm not sure if I should be looking to obtain a new unit or get the head examined/replaced.

I'm tempted to run the drive over the next two months with a two week cycle of tapes (one week new tapes, second week old know good tapes) and monitor the error rates as reported by LTT after each job. At the end of each week using new tapes use a cleaning tape (that would equal to 4 cleaning cycles over the two months, hopefully this is not excessive as I do not want to damage the heads due to over cleaning).

Hopefully this action will nurse the unit back to full health.

All that being said none of this is worth doing if the integrity is in doubt as the data is the most important factor. I have a SDLT offsite to do test restores with (I assume there is no risk of contaminating this unit?). All the tape drives are in normal office/home environments, whilst not clean room air filtered standards they are not smoke ridden dusty places.