One thing i want to add to the cleaning discussion.
If NetWorker is installed on a W2k server, NetWorker can actually handle
the cleaning signal from the device. In that case you get the best of
two worlds: Cleaning when needed, and NetWorker knows it is happening
and the cleaning does not disturb the running backups/restores.
Salvatore Buccoliero
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-----Oprindelig meddelelse-----
Fra: Davina Treiber [mailto:treiber AT HOTPOP DOT COM]
Sendt: 27. februar 2003 12:07
Til: NETWORKER AT LISTMAIL.TEMPLE DOT EDU
Emne: [Networker] Drive cleaning
I'd like to revisit the age old discussion about the best way to do
drive cleaning. I'm working at a site with a large number of tape
libraries of various sizes, mainly from StorageTek, but also some older
ADIC units. The drives are DLT7000 gradually migrating to LTO. They
currently use NetWorker cleaning on most of these and we are trying to
establish the best strategy. Here is my attempt to be objective about
the pros and cons of the two possible approaches, as well as my own
opinion. I would be very interested to hear what the NetWorker community
think about this emotive issue. Some views from Legato staff would also
be welcome.
NetWorker controlled cleaning.
NetWorker is configured to clean drives at set intervals of elapsed
time. The cleaning tape(s) is/are stored in a designated tape slot
within the range normally used for data tapes. The number of cleaning
tape uses is configured within NetWorker. When a cleaning tape is used
up, a notification can be sent from NetWorker.
Library firmware controlled cleaning.
The library firmware is configured to clean drives on demand. The DLT or
LTO drives are sophisticated enough to send a signal to the library when
cleaning is needed, and the library automatically loads and unloads the
cleaning tape at exactly this time. The cleaning tape(s) is/are stored
in dedicated cleaning slots (library dependent). The number of cleaning
tape uses is configured in the library firmware. When a cleaning tape is
used up, most libraries withdraw the tape to the CAP and display a
message on the library front panel, this may be accessible remotely if
the library has remote management software and a network connection.
What is wrong with NetWorker controlled cleaning?
* The cleaning is based on an elapsed time since the last clean, e.g.
two weeks. This takes no account of the drive usage in this time, a
heavily used storage node drive may have had perhaps 168 hours of use in
that time, whereas a drive attached to an application server may have
only had perhaps 14 hours use. It is highly likely that the former case
would have required a clean before that time, but unlikely that the
latter case is anywhere near to needing a clean.
* Cleaning a drive before it is required is wasteful of cleaning tapes
and can be bad for the drive. DLT drives need infrequent cleaning, LTO
drives rarely need cleaning at all.
* A heavily used drive may require cleaning before the cleaning interval
is reached. It will not get cleaned on demand, and may cause errors or
damage to data tapes. You can clean manually if there are errors but
this is not ideal on a remote site because unless you can actually see
the library you don't know whether the error was caused by the need to
clean or some other problem.
* One or more data slots are lost due to the need to store cleaning
tapes.
* Because cleaning tapes are in data slots, you must take care to
specify a slot range to avoid the cleaning tapes when inventorying the
jukebox.
What is wrong with library controlled cleaning?
* NetWorker may show an error on loading a tape when the library is
cleaning a drive. Usually these errors are recoverable without user
intervention.
* Cleaning tape usage data is only available from the library front
panel. Some libraries have remote monitoring software available, but
this requires a network connection which may not have been set up. Even
with remote monitoring software, it requires pro-activity, to go and
check usage rather than being automatically alerted.
* When a drive goes bad, it may repeatedly request cleaning and use up a
cleaning tape. NetWorker cleaning would just show errors. Which is
worse?
* Not all libraries support this feature.
Legato Support always recommended using library firmware cleaning where
available in pre 6.x days. Now it seems that they are recommending
NetWorker cleaning instead. I don't understand the reason for this
U-turn, since all the disadvantages listed above still apply. I firmly
believe that library firmware cleaning is superior to NetWorker
cleaning.
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