Brian,
How did you get the latency
figure? Also, what versions of Oracle and Digital UNIX are you running.
Is there any more info on this at the Oracle or Compaq web sites?
Thanks
Edina De Simone
-----Original Message-----
From:
alpha-osf-managers-owner_at_ornl.gov
[mailto:alpha-osf-managers-owner_at_ornl.gov] On Behalf Of Brian Milnes
Sent: Sunday, March 14, 1999 10:04 PM
To: alpha-osf-managers_at_ornl.gov
Subject: Oracle over Advfs over
Raid5 considered dangerous
Judith,
We've have very very bad write latency
on Oracle over Advfs (over 400
ms) due to write sequentialization on
writes to a single file. This
was terrifically difficult to localize,
but reading Oracle's write
time counters after building a new
tablespace will give you a feel for
its impact in your configuration. I
would certainly recommend that any
database that requires high write rates
not be run on Raid5 or Advfs.
Their combination could really give you
trouble particularly during
partial stripe writes.
If you must do this for cost efficiency
I would spend some time
understanding your write load and
optimizing your Raid5/Advfs/Oracle
for it. You may try to get a nice small
stripe that minimizes partial
writes. I would also keep your Advfs
domains down in size (to minimize
recovery time) and most critically I
would never execeed about 100 MB
on a single data file. You will also
need to run multiple database
writers as you can not run asynchronous
IO.
The Oracle MetaLink pages are now
filled with warnings on our
experience. Compaq acknowledges the
problem and the write
sequentialization will be removed in a
future release of the 5 stream.
-Brian Milnes
Systems Engineer
Amazon.Com
Received on Mon Mar 15 1999 - 15:05:06 NZDT