System very slow. High %wio

[Marco Queirolo]

Hello,
I'm running HP-UX 11.0 and Oracle 8.1.7. The system run very slow.
The %wio is very high (95%-100%). The major disk activity is about 1000 bps.

The system is running mirror disk.


Best regards.

Marco.

[Bill McNAMARA_1]

lvdisplay the mirrored lvs to check options
check filesystem mount options with
mount -p

Later,
Bill

[Stefan Farrelly]

Youre completely i/o bound. You need to look into adding more disk controllers, faster disks, or striping your lvols across as many controllers and disks you can get. If youre using an external disk array stuff it full of memory cache. These are the only ways to get your wio% down to a more reasonable level (<10). Either that or reduce the number of users on your server because it just cant cope with that many i/o requests (any wio% > 20 is really bad).

[Sridhar Bhaskarla]

Hi Marco,

Use either glance or sar -d to identify the disks that are heavily used. You can find out the logical volumes if you have glance. Shuffle the data to other disks that not heavily used.

You will need to start considering lvm striping. Explore the other options that come with OnlineJFS like convosync=direct, mincache=direct, delaylog etc.,. and apply that fit best for you.

Also make sure that the load is balanced across both the controllers (if you are using alternate paths). You can alter the links using either pvchange or a vgreduce followed by a vgextend. With LVM striping you can achieve best possible load balancing with default tools.

Also make sure your buffer cache is not way too much. Adjust your dbc_max_pct to get around 400MB.

-Sri

[Robert Thorneycroft]

You should also look into:

a) Tuning your application. Full tablescans running repeatedly can really mess your IO.

Increasing the memory available to the SGA Buffer Cache, this will result in more data being held in memory, and therefore less disk activity, whilst at the same time giving your performance a nice boost.

I would strongly recommend that you look at the Oracle 8 Advanced Tuning books as these will walk you through the whole tuning exercise.

When I spent a couple of weeks reading these books the average response time on my SAP system droppped from almost 1 second to less than 500ms, not bad for a book that cost about ??40.

Kind regards,

Robert Thorneycroft

[Robert Thorneycroft]

Almost forgot you might also want to make sure that you have not got any hardware errors on the disks / controllers which are responsible for the high wait I/O. A disk that it on its way out or a dodgy SCSI controller will pretty much bring a database to its knees.