SAS array boot drives

[Rick Garland]

Hi all:

Have a rx3600 with P400 HW RAID controller. HPUX 11.23

ioscan -fnCescsi_ctlr
I get the SAS Adaptor at /dev/sasd0

A physical look at the system shows 2 hot-swap/hot plug drives in the chassis. There are slots for a total of 8 drives, the other 6 slots are empty.

sasmgr get_info -D /dev/sasd0 -q phy=all
shows PHY 4&5 UP while others (0,1,2,3,6,7) are DOWN.
sasmgr get_info -D /dev/sasd0 -q raid=all
shows 2 participating physical drives (the same PHY drives as listed above) defined as 1 LOGICAL DRIVE. This LOGICAL DRIVE lists PHY5 as primary and PHY4 as secondary. It is RAID=1

On the OS/LVM level I see 1 device from ioscan. The lvdisplay shows 0 mirror (no mirrorUX, of course.) The lvlnboot -v shows only 1 device.

How do I determine that there are multiple boot/root disks to boot from? How do I tell if they have the proper configuration to boot the ALT in case of disk failure?

Thanks

[Patrick Wallek]

As far as LVM is concerned, you only have a single boot drive. This drive is your LOGICAL drive. This logical drive, however does contain your 2 physical drives. You don't have to set up multiple root/boot drives in this case.

Theoretically you should be able to pull either drive 4 or drive 5 from its slot and your machine should keep running and should boot. All the work of determining which drive to use is being done in the background by the RAID controller.

[Sameer_Nirmal]

As Patrick said Logical drive device comes into picture in case of HW RAID controllers. The logical drive acts as metadevice which talks to the physical drives underneath it through it's own internal mechanism. Thus from LVM/HPUX loader perspective, a logical drive would act as a primary boot device.

You might want enable "Auto-Fail Missing Disks at Boot".

Take a look at this link for HP's recommendations.

http://docs.hp.com/en/J6369-90037/ch03s09.html

[Rick Garland]

So this is the configuration to look for.

Another question; How to know which PHY drive the system booted from? I know the OS is seeing 1 disk drive - this is the Logical drive. Behind the scenes the HW controller has 2 physical drives and these are configured in RAID=1. If, as in my situation, the PHY5 drive dies and the system reboots on PHY4 - how do I determine that such an event happened and I do I determine which PHY disk is the problem? If a disk needs to be replaced how do I know which disk?

[Patrick Wallek]

With this set up though, if one drive of your RAID set fails, your machine should not reboot. It should keep right on going.

I don't think there is really a way to tell which physical drive the logical drive is using.

HP-UX will make a request to the logical drive and the RAID controller will take that and do the appropriate actions. If one of the physical drives is bad, the RAID controller should mark it as such, but this should never impact HP-UX itself.

Think of it along the same lines as using a disk array. You present a LUN to HP-UX LVM. LVM sees the LUN as a single device, but on the array it may be striped across 6 disks. HP-UX doesn't care. This is the same thing.

You are trying to think of this in terms of traditional HP-UX MirrorDisk mirroring and it is not the same thing.