[gpfsug-discuss] mmapplypolicy didn't migrate everything it should have - why not?

[Marc A Kaplan]

ANYONE else reading this saga?  Who uses mmapplypolicy to migrate files 
within multi-TB file systems?  Problems? Or all working as expected?

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Well, again mmapplypolicy "thinks" it has "chosen" 1.6 million files whose 
total size is 61 Terabytes and migrating those will bring the occupancy of 
gpfs23capacity pool to 98% and then we're done.

So now I'm wondering where this is going wrong.  Is there some bug in the 
reckoning inside of mmapplypolicy or somewhere else in GPFS?

Sure you can put in an PMR, and probably should.  I'm guessing whoever 
picks up the PMR will end up calling or emailing me ... but maybe she can 
do some of the clerical work for us... 

While we're waiting for that... Here's what I suggest next.

Add  a clause ...

SHOW(varchar(KB_ALLOCATED) || ' n=' || varchar(NLINK))

before the WHERE clause to each of your rules.

Re-run the command with options  '-I test -L 2'  and collect the output. 

We're not actually going to move any data, but we're going to look at the 
files and file sizes that are "chosen"...

You should see 1.6 million lines that look kind of like this:

/yy/dat/bigC     RULE 'msx' MIGRATE FROM POOL 'system' TO POOL 'xtra' 
WEIGHT(inf) SHOW( 1024 n=1)

Run a script over the output to add up all the SHOW() values in the lines 
that contain TO POOL 'gpfs23capacity' and verify that they do indeed
add up to 61TB...  (The show is in KB so the SHOW numbers should add up to 
61 billion).

That sanity checks the policy arithmetic.  Let's assume that's okay. 

Then the next question is whether the individual numbers are correct... 
Zach Giles made a suggestion... which I'll interpret as 
find some of the biggest of those files and check that they really are 
that big....

At this point, I really don't know, but I'm guessing there's some 
discrepances in the reported KB_ALLOCATED numbers for many of the files...
and/or they are "illplaced"  - the data blocks aren't all in the pool FROM 
POOL ...

HMMMM....  I just thought about this some more and added the NLINK 
statistic.  It would be unusual for this to be a big problem, but files 
that are hard linked are
not recognized by mmapplypolicy as sharing storage... 
This has not come to my attention as a significant problem -- does the 
file system in question have significant GBs of hard linked files?

The truth is that you're the first customer/user/admin in a long time to 
question/examine how mmapplypolicy does its space reckoning ... 
Optimistically that means it works fine for most customers... 

So sorry, something unusual about your installation or usage...





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