Linux – CentOS 7 mpath Install, Can’t Find /dev/centos/root


I am attempting to install CentOS 7 on an older SuperMicro H8QM8 motherboard (AIC-7902 SCSI controller, aic7xxx kernel module) with 3 attached drives. The Adaptec SCSI bios recognizes the drives and they have each been low-level formatted via the SCSI bios.

On using the CentOS GUI install to configure the hard drive layout, the installer detects the SCSI devices as a single mpath device (is this normal?), however there a comment on the single mpath device sda, sdb, and sdc. I seem to be able to successfully set up a partition table on a drive, but (at this point) I'm not sure exactly which drive I'm working on.

After the system reboots, I get an error about not finding /dev/centos/root and also not being able to find /dev/by-uuid/blahblahblah and get dropped into the dracut shell. I am able to confirm that (at this point) the aic7xxx, scsi_*, and dm_* modules are loaded via a kmod list but don't see the various HD nodes that the boot sequence was looking for. In /dev I see /dev/sda, /dev/sdb, and /dev/sdc, but no more specific partition nodes (i.e. /dev/sda1). I don't seem to have access to fdisk at this point, so I can't see which SCSI drive has the partition table, however the log shows that "something" detected that /dev/sda has 3 partitions.

So then I reboot with the CentOS 7 CD in rescue mode, and the rescue boot successfully detects and mounts all my partitions under /mnt/sysimage. At this point, I can see that the parititon table, file systems, and installed files all went to /dev/sda (/dev/sda1 for /boot, /dev/sda2 for lvm).

So there are a two sub-questions, but perhaps I don't quite know how the multipath works and it is just a single question:

  • Why are the 3 drives displayed as a single mpath device in the installer? In the installer, is there a way to address a single drive (e.g. /dev/sda) instead of the mpath device as a "whole"?

  • Why can the installed system not find the parition table on /dev/sda? What information can I use (perhaps from the dracut emergency prompt) to further debug?

Best Answer

Passing the "nompath" option to the boot kernel (anaconda) solved my problem, as apparently the mpath recognition was a false positive. Once I did that, everything proceeded normally, with individually addressable drives.

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