On Friday, Apr 25, 2003, at 09:46 Australia/Sydney, David Bronder wrote:

Wilcox, Andy wrote:

Good observation there Paul, I just haven't noticed... but as you
quite
rightly say, direct I/O is enabled by default... I am still curious
about
the AIXASYNCIO option and whether or not that can provide any
advantages or
disadvantages... Hopefully I will have some findings in the very near
future
and I will let you know.

Based on information in the Redbook "IBM Tivoli Storage Manager Version
5.1 Technical Guide Redbook" (SG24-6554-00) and feedback from a PMR
that
I opened, there are a couple of limitations of note with AIXASYNCIO and
AIXDIRECTIO options.

Direct I/O only works for storage pool volumes.  Further, it "works
best"
with storage pool files created on a JFS filesystem that is _not_ large
file enabled.  Apparently, AIX usually implicitly disables direct I/O
on
I/O transactions on large file enabled JFS due to TSM's I/O patterns.
To ensure use of direct I/O, you have to use non-large file enabled
JFS,
which limits your volumes to 2 GB each.

That's a real shame, IMHO. I notice that open(2) doesn't mention any
special handling of O_DIRECT between open and open64. I'd say most
TSMers
would have their stgpool volumes bigger than 2 GB.

Asynchronous I/O supposedly has no JFS or file size limitations, but is
only used for TSM database volumes.  Recovery log and storage pool
volumes do not use async I/O.  AIX 5.1 documentation mentions changes
to
the async I/O interfaces to support offsets greater than 2 GB, however,
which implies that at least some versions (32-bit TSM server?) do in
fact have a 2 GB file size limitation for async I/O.  I was unable to
get clarity on this point in the PMR I opened.

Well, looks like AIX has had large file AIO support since large file
support was added (4.2.1, from memory). I see the matching routine
definitions aio_write and aio_write64 on a 4.3.3 system. It should just
depend if TSM was compiled with _LARGE_FILES defined or not.

I'd run a trace on dsmserv, but ours are on Solaris...

Cheers,
--
Paul Ripke
Unix/OpenVMS/TSM/DBA
101 reasons why you can't find your Sysadmin:
68: It's 9AM. He/She is not working that late.
-- Koos van den Hout