I have used both DDX and MDX for years (at least 10), without problems.  I will say that you should monitor the MDX for expansions occurring, and change the capacities to re-hash the masters if an expansion does occur, as this can get quite inefficient very quickly.  It both saves disk space, and prevents "gotcha" moments.  I would not worry about small increments and fragmentation - generally speaking fragmentation is a good thing across drives.  Large increments introduce LONG pauses, so be careful.  A larger issue is to make sure your datasets are blocked properly so that you get the most bang for your buck on disk reads.

Wyell Grunwald

-----Original Message-----
From: HP-3000 Systems Discussion [mailto:[log in to unmask]] On Behalf Of Mark Landin
Sent: Thursday, April 07, 2011 10:18 AM
To: [log in to unmask]
Subject: Dynamic Dataset Expansion

Now that we are flush with disk space (discfree shows 179,000,000 sectors
free), we'd like to enable DDX and MDX on our main MANMAN databases.

Are there any serious "gotchas" with doing so? I know it's key to strike a
balance between a small increment (which will cause greater disk
fragmentation) and a large increment (which runs the risk of failing to
acquire enough disk space, as well as lengthening the pause while the
expansion happens), but are there any other key considerations we must look
at?

-- 
"He's old enough to know what's right and young enough not to choose it.
He's strong enough to win the world and weak enough to lose it." - Neal
Peart

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