DATMAN TECHNICAL BULLETIN #036
From: Kan Yabumoto tech@datman.com
To: DATMAN user
Subject: How often does the tape drive head need to be cleaned?
Date: 1999-12-01
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The following questions are asked quite frequently:
How often should I clean the tape head?
Yet, we do not hear a consistent answer to that. This article
examines this common question by studying what the various DDS
drive manufacturers are saying in their literatures.
Hewlett Packard, the leader in the DDS technology states in its
manual the following recommendation.
Cleaning Regime:
HP recommends a preventative head-cleaning regime to maintain
reliable operation and performance of DDS-format drives.
It is not satisfactory to wait for front panel Caution Signals
to advise that the heads should be cleaned; by the time this
signal appears, performance may have already been impaired.
However, if the Caution Signal appears, head-cleaning should
be the first action to take.
The following table provides a guide for a sensible cleaning
regime which in no way damages or shortens the life of either
the drive mechanism or the tape heads:
Tapes used per day <= 1 2 3 4 5
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Cleaning interval weekly twice twice daily daily
weekly weekly
To clean the heads:
1. Insert a Cleaning Cartridge. The drive automatically
takes the cartridge and cleans the heads.
2. After about 30 seconds, the cartridge will be ejected.
3. Take the cartridge and write the date on it, so that
you have a record of how many times the cartridge has
been used. Cartridges can be used about 25 times before
they reach the end of their useful life.
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Caution: If the cartridge is ejected after only about 14
seconds, the cartridge has reached the end of its
useful life, and no cleaning has occurred. If this
happens, discard the cartridge and use a new one.
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(Note: the above section of this article was reproduced word-by-word
from Hewlett-Parkard's DDS Technical Manual, with a permission
granted by Hewlett-Packard.)
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Let me add a few observations of our own. As you can see HP's
recommendation in a very imprecise language, twice weekly and daily.
The chart does not distigush heavy usage of several hours and light
duty usage of several minutes a day. By using our imagination, we
may translate one "usage" to one two-hour run of a backup operation.
Once a day of such usage corresponds to a weekly cleaning. Here, the
manual often assumes the usage is predominantly for a corporate file
server backup operation. That is 5 business days a week. Therefore,
it suggests 10 hours of usage per head cleaning. This is the latest
HP recommendation on the subject which appears consistently on many
if its publications. We find the passage in HP's publications as
early as in 1995.
But, when we examine HP's 1993 publication, we find their recommended
interval of 25 hours of tape use. This is usually measured by the
active tape read/write operation excluding the idle time. We are not
sure why HP shortened their recommended interval from 25 hours to
10 hours or so in just two years. Seagate's Product Description Manual
for their DDS drive also says 25 hours of read/write operations whereas
WangDAT's manual states the cleaning interval should be 8 to 10 hours
of tape motion.
Finally, Sony has its own unique approach. Sony drives come with
three LEDs as opposed to two with most other brands. It indicates
media warning signal with the 75% duty-cyle flashing of the "Tape"
(middle) LED when the tape has an excessive error rate. It also
starts the 75% duty-cycle flashing of the "Status" (right) LED after
24 hours of drum rotation (which is almost the same thing as the
read/write action) has elapsed since the most recent head cleaning.
Here, Sony's approach seems more precise because the drive measures
the interval and lets the user know when it is time to clean the head.
This contrasts with HP's strategy where the LED flashing was only
activated when the firmware suspects the dirty head is the cause of
the current problem. HP recommend the user keeps track of the head
cleaning regime before too late ----- quite often, some corrupted
tape makes the drive firmware believe the current read problem can
be solved by cleaning the head!!!
When we compare the various manufacturer's guidelines, the closest
thing to a consensus is approximately 25 hours of read/write
operation. At any rate, we believe none of their recommendation
is based on very strict and scientific data. We all know we should
clean the head every once in a while.
Here are some additional facts about the drives:
All DDS drives have a self head-cleaning mechanism. When the
firmware detects some kind of error, you may hear some clicking
noise from the drive which is the sound of self-head clening.
The head cleaning operation by a cleaning cartridge operates by
moving a very fine polishing surface around the head just like
the regular tape surface would touch. The drive ejects the
cleaning cartridge without rewinding the tape. When it reaches
the end it should be discarded.
The length of head cleaning cartridge varies widely by the
manufacturers. Sony's cleaning cartridge (DDS 5CL) comes with
5 meter cleaning tape whereas Maxell's cartridge (HS-4/CL) has
12 meter tape. HP's clearner is believed to be manufactured
by Maxell.
Although HP's manuals always say that a cleaning cartridge can
be good for 25 cleaning operations, we have never compared the
actual speed of the cleaning pass and the duration of the cleaning
action from one HP model to another, it is difficult to believe
that all drives with all brands of cleaning cartridge are good
for exactly 25 cleaning operations.
Probably it is a self-defeating act when you manually rewind the
head cleaning cartridge and reuse the same surface for more than
one pass.
Conclusion:
If you like to be very conservative, clean the head every day.
If you are pragmatic and budget conscious, do it once a week.
If you are stingy, do it once a month. If you don't remember
how long ago your last cleaning was, you should do it now.