Finally got this solved.  I had two issues. The i/o errors were because I wasn't loading the scsi_dh_rdac module (mentioned in passing in the owners manual).  That's done in RHEL6 by creating /etc/sysconfig/modules/scsi_hd_rdac.modules with these contents: #!/bin/sh exec /sbin/modprobe scsi_dh_rdac >/dev/null 2>&1 And make the file chmod +x. The multipath issue was with my conf file.  I had copied it from a PDF on Dells site (www.dell.com/.../powervault-md36x0i-linux-dm-installation.pdf) and hadn't changed the name of the array, so had MD32xxi instead of MD36xxi.  This is the /etc/multipath.conf file I'm using that works: defaults {   user_friendly_names yes  max_fds 8192 } blacklist {   device {                 vendor "*"                product "Universal Xport"  } } devices {   device {             vendor "DELL"            product "MD36xxi"            path_grouping_policy group_by_prio            prio rdac             path_checker rdac            path_selector "round-robin 0"            hardware_handler "1 rdac"            failback immediate            features "2 pg_init_retries 50"            no_path_retry 30            rr_min_io_rq 100  }  device {             vendor "DELL"            product "MD36xx"            path_grouping_policy group_by_prio            prio rdac             path_checker rdac            path_selector "round-robin 0"            hardware_handler "1 rdac"            failback immediate            features "2 pg_init_retries 50"            no_path_retry 30            rr_min_io_rq 100        } }
I have a new MD3600i with two controllers and two NICs each: 172.16.6.6 ctrl 0 port 0 172.16.7.6 ctrl 0 port 1 172.16.6.7 ctrl 1 port 0 172.16.7.7 ctrl 1 port 1 And I have a Redhat Enterprise Linux 6.3 host with a nic on both of those subnets. 172.16.6.40 172.16.7.40 I installed the Dell MDSS software and used the configuration utility to configure the host using both controllers.  Then assigned four virtual disks to it. Now, when I reboot or run fdisk -l, or try to use multipathd, I get a bunch of stuff like this in the terminal or the console: /dev/sdb: read failed after 0 of 4096 at 0: Input/output error /dev/sdb: read failed after 0 of 4096 at 27000504123392: Input/output error /dev/sdb: read failed after 0 of 4096 at 27000504180736: Input/output error /dev/sdb: read failed after 0 of 4096 at 4096: Input/output error /dev/sdc: read failed after 0 of 4096 at 0: Input/output error /dev/sdc: read failed after 0 of 4096 at 27000504123392: Input/output error /dev/sdc: read failed after 0 of 4096 at 27000504180736: Input/output error /dev/sdc: read failed after 0 of 4096 at 4096: Input/output error multipath -ll looks like this for each of the four devices: So the errors above are coming from the two sd:emotion-30: devices that go to the second controller. Is there a way to fix these errors?  I've been digging through multipathd documents (found some changes to /etc/multipath.conf for rhel5, but not sure it's relevent for rhel6), but I'm getting it even with just fdisk.  Is this just expected behavior?
MD3600i linux multipath on RHEL 6.3