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.

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.

=Dave

--
Hello World.                                    David Bronder - Systems Admin
Segmentation Fault                                     ITS-SPA, Univ. of Iowa
Core dumped, disk trashed, quota filled, soda warm.   david-bronder AT uiowa 
DOT edu