Brown, Ed wrote:
>
> I tend to agree with this point.....
>
> > Raw vs JFS is an interesting issue.  Up until now I've gone RAW (on
> > everything)
> > since it is quicker to setup and is higher performance.  Now however I
> > have been
> > informed that database corruption can occur if a second server
> > instance is started
> > (no mention of storage pool space but it would appear to be subject to
> > the same
> > problem).
> >
> > Furthermore, according to an internal but third party source, AIX RAW
> > device code is
> > not being improved while JFS performance is.
> > Now I'm leaning toward JFS
> >
> This is very interesting, and it seems to make sense. I sounds similar
> to the thought
> of putting highly accessed files toward the center of the disk for
> highest average
> access.
>

Improving the performance of JFS only lowers the overhead that JFS adds
on top of the LVM.  That is, the JFS has the same LVM overhead beneath
it as any application that uses raw logical volumes.  Perhaps the JFS
could re-arrange write order more intelligently than an application
(ADSM) to take advantage of variation in disk readiness, using the
journalling to ensure data integrity with asynchronous writes, but I'm
not sure it actually runs that way.  ADSM probably wants to assume
synchronous writes for its own data integrity (i.e. if it writes block X
before Y, it assumes that in the event of a crash where not all data is
written to disk, there is never the case where block Y was written when
X wasn't).  At least that should apply to mirror copies of the log when
sequential writes are chosen.

With respect to corruption with a second server, should not the locking
of access to JFS files be the same as locking of access to the device
special files that an application opens to access the raw logical
volumes?  That is the whole point of accessing character-mode devices
through the filesystem; you can treat it like a file, for the most part.

One advantage of having a JFS is protection from system crashes
corrupting the log and database.  ADSM is currently vulnerable to
(some?) partial page write problems which JFS would presumably lower the
chances of occuring relative to raw since it is journaled.

Anyone who understands the details care to correct my ramblings?

Cheers...
Bruce