Greetings, everyone.
We are having issues with some Oracle databases on ZFS. We would appreciate any
useful feedback you can provide.
We are using Oracle Financials, with all databases, control files, and logs on
one big 2TB ZFS pool that is on a Hitachi SAN. (This is what the DBA group
wanted.) For the most part, the system runs fine.
When the DBA’s do clones or backups using RMAN, however, all of the write
activity almost freezes the system. The regular transactions back up, screen
refreshes get delayed, etc. The system, quite simply, grinds almost to a halt.
The immediate issue seemed to be the log file writes. If we separate the logs
space, it just shifts the problem to the DB/control files. If we split out the
backup space, things are OK during the RMAN backups, but the problems remain
for the clones/restores. The issue seems to be serious write
contention/performance. Some read issues also exhibit themselves, but they seem
to be secondary to the write issues.
We ran a test doing this for one environment on a test UFS LUN. While both the
backup and restore operations took twice as long, we did not have the system
lock issues we see with ZFS.
We’ve also been playing a little with ztune.sh on a test system, but we really
need to come to a proper solution (and a better understanding of what is
causing the problems). Can anyone explain to us why the writes are backing up
like this, and what we can do about this? Under Solaris 8, VxFS worked just
fine in this scenario. Due to the number of files, UFS was not an option. Since
the environment is going to RAC in six months, upgrading Veritas did not seem
like a justifiable option, with the (mistaken?) belief ZFS performance would be
more than adequate.
Thank you for any help you can provide.
Rainer
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