IT Infrastructure – The Infinite Source of Puzzles

We will begin with a quick mention of the problem currently under investigation with EMC support:

• Host: Dell PowerEdge R710, PowerPath, RHEL 4.8.
• SAN: Clariion CX4-120
• Connectivity: iSCSI – two ports per SP, two ports on the host, two VLANs on Nortel ERS5520.

Problem: if we present two LUNs to the host, put them into a single VG, then create an LV with no striping (LUNs get concatenated on that volume), everything is good. If we take the same LUNs and put them into a striped LV per various EMC Best Practices documents (since the LUNs themselves are striped across physical disks EMC calls this layout “plaids”), read performance suffers in a very bad way, dropping to about 4MB/sec. Write performance stays perfect at over 100MB/sec.