SVM V20z root mirror panic

One of the problems I have been working on recently has to do with running Solaris Volume Manager on V20z and V40z servers. In general, SVM does not care what kinds of disks it is layered on top of. It justs passes the I/O requests through to the drivers for the underlying storage. However, we were seeing problems on the V20z when it was configured for root mirroring.

With root mirroring, a common test is to pull the primary boot disk and reboot to verify that the system comes up properly on the other side of the mirror. What was happening was that Solaris would start to boot, then panic.

It turns out that we were hitting a limitation in the boot support for disks that are connected to the system with an mpt(7D) based HBA. The problematic code exists in bootconf.exe within the Device Configuration Assistant (DCA). The DCA is responsible for loading and starting the Solaris kernel. The problem is that the bootconf code was not failing over to the altbootpath device path, so Solaris would start to boot but then panic because the DCA was passing it the old bootpath device path. With the primary boot disk removed from the system, this was no longer the correct boot device path. You can see if this limitation might impact you by using the "prtconf -D" command and looking for the mpt driver.

We have some solutions for this limitation in the pipeline, but in the meantime, there is an easy workaround for this. You need to edit the /boot/solaris/bootenv.rc file and remove the entries for bootpath and altbootpath. At this point, the DCA should automatically detect the correct boot device path and pass it into the kernel.

There are a couple of limitations to this workaround. First, it only works for S10 and later. In S9, it won't automatically boot. Instead it will enter the DCA and you will have to manually choose the boot device. Also, it only works for systems where both disks in the root mirror are attached via the mpt HBA. This is a typical configuration for the V20z and V40z. We are working on better solutions to this limitation, but hopefully this workaround is useful in the meantime.
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