Is there a way to force an Ultrium 1 drive to request a clean?

[Timothy Curtis]

Hi there, I'm supporting a service call on a StorEdge L700 (rebadged Storagetek L700) with 8 HP LTO Gen1 drives.

There have been cleaning issues, not the least of which was a universal cleaning cartridge with an HP cleaning cart barcode (CLN001) on it. The library spat the dummy and wouldn't use the tape. I instructed the field engineer to put the correct bar code on it (CLNUxx) and import it into the library again. So far so good.

Due to the cleaning issue, five drives have been replaced in this library, so they're all brand new at this stage... but I want to somehow make one of the drives request a clean so that next time the backup software attempts to mount that drive, the library interrupts and runs a clean on it. Is this possible?

[Luk Vandenbussche]

Which backup software are you using?
On which OS is the backup software running

[Ralf Loehmann_2 · Accepted solution]

Hello Timothy,

to answer your question, it might be possible to set a cleaning flag in the backup application, but the drive still might not clean as you expect.

Here some small background about cleaning on the HP LTO drives and some advices.
First you should never use automatic cleaning of the library. Better use the cleaning mechanism of the backup software, which nowerdays checks the tape alert flag.
Second thing here, even if you insert an cleaning cartridge in the drive you might not see any cleaning with this tape, the reason for that I will add at the end.
The only problem you might have with the generation 1 drive and the Universal Cleaning cartridge is that you need a newer firmware version, at least E20D.

If you think that you have drive problems you might check with the HP StorageWorks LTT tool: http://h18006.www1.hp.com/products/storageworks/ltt/index.html

This contains an LTO Acceptance test, which would show if your drives have any problems. If this test passes, your drive is ok and there might be an missunderstanding how cleaning works.


Here the background about preventing excessive cleaning operation and information about the internal Head cleaner of the drive:

Preventing Excessive Cleaning Operation


The firmware performs a check to prevent excessive cleaning being forced upon
the drive. Unnecessary cleaning shortens the useful life of a cleaning cartridge as
well as risks degrading drive performance.
The excessive cleaning criteria is met if the following is TRUE:
* Cleaning LED is not turned on.
* Tape Alert flag 20 is not set.
* Cleaning operation has been performed in the last 336 hours (2
weeks) since the drive was powered on.
If the firmware detects the above condition is true after a cleaning cartridge has
been inserted, then

a) The internal head cleaner is activated to brush the heads.
b) Estimated Cleaning Usage in the cartridge CM remains the same. I.e. not decremented.
c) Cleaning tape is not threaded.
d) Cartridge is unloaded (if applicable)* after internal head cleaning has
completed its operation.


* Certain automation/library usage
environment requires the drive not to
unload the cartridge unless it
specifically requested by the host.




New Internal Head Cleaner
Preventative Cleaning Using the Internal Head Cleaner
The internal head cleaner is a brush that can be drawn over the heads to 'scrub'
away loose debris. It is designed to operate in conjunction with the head contour
for trapping and removing media debris. It is non-abrasive to the head and thus
can safely be used as frequently as required.
Using fibers that are electrostatically dissipative and also have a conductive coating provides ESD protection. In addition the brush assembly sits inside a
conductive plastic channel to assist bleeding any conductive charge off the
head.
The internal head cleaner is used:
1. Immediately after using a cleaning cartridge.
2. When a cleaning cartridge is being used too frequently. The drive
performs an internal head clean instead of a clean using the loaded
cleaning cartridge.
3. As part of error recovery algorithm. For example, if multiple read retries
have failed, the tape is unthreaded, the internal head cleaner is operated
to remove loose debris, then the tape is re-threaded, and retries begin
again.
4. After an unthread, if more than 150 thousand meters of tape have been
pulled since the last use of the head cleaner.
5. When the drive detects more than 10% error rate variation between the
channels.

[Timothy Curtis]

Hi Ralf

Thank you very much for your reply.

[Timothy Curtis]

One more question - what criteria are used by an HP Ultrium drive to determine that cleaning (with a cleaning tape) is required?

Thanks
Tim

[Ralf Loehmann_2]

Hello Tim,

sorry there is no much information about that available, most of that is kept internal.

The drive will decide that cleaning is required if it has been unable to complete a write operation because it could not verify that the data has been written to tape successfully. This is after all retries have been exhausted.
If the cleaning is required, the following actions will result:
The 'cleaning required' LED on the front panel will be lit.
The appropriate TapeAlert flag is set. This state will only be cleared once the drive is cleaned by inserting a cleaning cartridge. This state will be maintained across power cycles.


That is what I found, this means after all internal recoveries, specially with the internal head cleaner, it will set the Cleaning required.

Her something more:
Cleaning Algorithm
The cleaning algorithm used is critical to the effectiveness of the cleaning operation in removing the debris from the head/tape interface. HP has developed a unique algorithm that gives the maximum benefit from the cleaning tape.
The use of a cleaning tape will always be a compromise. On the one hand you need to ensure the heads are cleaned properly, whilst on the other hand you need to ensure that the drive is not adversely affected in any way. With a very aggressive cleaning algorithm the heads would be clean but the Error Rate margin could be affected due to Pole Tip Recession of the heads, whereas with a passive cleaning algorithm the heads will not be cleaned properly and multiple cleaning operations may be required to get the heads clean.
The performance of the cleaning algorithm is directly related to the amount of tape that is used in each cleaning operation. In the HP Ultrium tape drive the cleaning algorithm uses 18m of fresh tape per clean to maximize the cleaning effect, and to provide the area needed to transport the debris out of the drive, but at the same time ensuring that there are no adverse effects such as Pole Tip Recession. Also to protect from over cleaning the HP drive will not utilize a cleaning tape again until at least 336 hours (2 weeks) has elapsed. In addition the
head structure is made of an extremely hard and durable ceramic material called Cermet, the same material disk drive heads are made from. As a result, the HP Ultrium head is not
susceptible to wear problems. The only exception to the 336 hour rule is if the drive is requesting a cleaning cartridge be
used or the drive has been power cycled since the last clean. Normally if a cleaning cartridge is loaded inside the 336-hour window then the drive will not thread the tape or increment the usage counter, but will operate the internal head cleaner.
In this way the HP Ultrium drive ensures that the cleaning algorithm is both effective at cleaning the heads whilst at the same time not adversely affecting the drive in any way.

Summary:
Cleaning with a cleaning tape is the last step in a long recovery procedure and because it is somehow destructive to the heads the firmware prevents the drive and the user to overdo it. Former technologies were using it much more often. On HP LTO drive (with internal cleaning mechanism) you might not see much request for cleaning at all. If cleaning might occur you might have a suspect tape media used and if cleaning occur a lot it is time to check the hardware. Probably than the error rates of the drives are that high that you would also see performance impact. In that case I would recommend to check with your support to not damage tape media with a defective drive. In an good environment with healthy tapes and working in a good performance range (to keep tape media streaming) you might not see cleaning at all.

I hope that helps a bit.