Tip:
Highlight text to annotate it
X
A dynamic archive is
different than a fixed archive. Dynamic archives are
used -- well, they are generally used for exceptional things,
not for day-to-day data collection.
And, in fact, we not, we do not really cover dynamic archives in any
detail in this class. It's more a part of our Advanced
Topics System Management Class. So it's usually something
that's created by the PI Server or the PI
Utilities themselves, that are used for
special circumstances. For example,
a piarchss can actually create a dynamic archive
when its doing -- it's being used as what we
call the offline archive in offline mode
to reprocess an archive. Now, what a dynamic
archive is, is it's an archive that simply does not
establish its full size, or its true size,
at the time at which it's initialized. When it's
initialized, we simply create a primary record for each tag
in the system that exists at that point, and then,
as we fill it with data, we simply add new overflow records,
not from the back of the archive
file, from the end of the file -- but we just add new primary rec...
New overflow records to the front of the file. So, in fact,
the dynamic archive, as its name
implies -- dynamic means it's going to grow in size
as you watch it. Now, we do have a relatively new
feature in which, if you are trying to write data to a
fixed archive that's in the past, not the Primary Archive,
if you are trying to write to the fixed archive
for a period of time that is expired,
and now let's say this is your, your third archive in the sequence,
we are automatically going to convert
that into a dynamic arc...archive if
you accidentally fill that archive. As I mentioned,
archives have a small amount
of free space in them for doing a moderate amount of modifications.
But, if for some reason you fill that entirely, we will simply
convert that over to a dynamic archive.
I want to warn you though, dynamic archives, unlike fixed archives,
they do not participate in the archive shift. So now,
this is going to result in having one more archive that cannot be
shifted into. You
can create these yourself using
this Archives plug-in in SMT. So you
can create this yourself, for example, to receive backfill
data from another historian or from a spreadsheet
or some other data store that you have got. Every once in a while, people will come to us
with, you know, these months and months,
or years' worth of data they'd like to backfill into the PI Server.
So, it's a good idea to, to use a dynamic
archive. You would be using that since you did not know,
you may not know exactly how many values you are going to get,
and you want to be as open-ended as possible
for that retrieval. So, those are dynamic archives. As I
said, we are not going to cover them in great detail in this class.