Disk performance issues with Oracle Linux?

While we ourselves did not have any performance issues of our Dell Poweredge 2950 using 2 Qlogic qle2460 HBAs to connect to an EMC DMX-3 SAN over Cisco FC switches, some of our colleagues at another subsidiary did have problems: only 50MB/s using the bonnie disk benchmark where we got 240MB/s... Clearly something was different.
Investigations showed they were using LVM on the LUNs and created partitions within LVM. We did not use LVM but gave bare LUNs to OracleASM to manage and control.

This led to believe that misalignment of the partition to physical disk cylinder may have caused additional overhead. Because LVM created an MBR on the disk's first set of cylinders, the first partition was created starting at cylinder 63. As this is not a power of 2, the disk subsystem experiences overhead as it translates the numbers back and forth. Research showed that both Oracle and EMC's best-practices both recommend to align your partitions on power of two cylinders! There is a best-practises for Oracle 10g and 11g white paper (PDF) by EMC, as well as an explaination about the misalignment issue from Bob Plankers.

No comments: