Mirroring OS

[Soheir Makhlouf]

In our environment, we install the OS on the SAN. each LUN consists of 4 disks where the OS is installed on one and mirrored to the other 3 using HW RAID. I have been told that mirroring the OS using SW RAID is more appropriate due to that on booting the server on OS failure, SW RAID is faster to discovering the drivers then HW RAID... Is is true? I run into this problem once when I was recovering from OS crach and booted from the internal disk not discovering the SAN disks fast enough

[Steven E. Protter]

Shalom,

Actually hardware raid is better, the I/O is taken care of by the Raid controller, either the one built in the system if you boot off local desk, or the SAN, if you boot off the SAN.

Software raid involves using CPU cycles to handle system calls and i/o as one disk mirrors to the other.

I don't think SW raid is going to discover drivers any faster than any other method. I doubt the issue you are experiencing comes from the speed the of discovery of SAN drivers.

Hardware discovery occurs when the kernel is booted.

In a hardware raid is in place and one of the drivers in the raid set fails, the boot occurs off the second disk in the set, which is transparent to the system.

In most scenarios the system may not even be able to tell the raid array is degraded until utilities are run (HP insight) to check it.

SEP

[likid0]

If you mean raid1 software array, a normal soft mirror has it's advantages, when you patch/upgrade,etc you can break the mirror and only make updates to one disk, in case of problems you can boot from the other disk.


When I use SAN disks(with raid5 or 10) as boot disks, I normally do a software raid1 mirror anyway or if I have 11.23/11.31 i use DrD with a nightly sync

[Chandrahasa s]

Hi,

Hardware raid in term of performance of system may help in very little extend.

If there is os patch activity on server if you found server is behaving badly after patching you dont have any option other then ignite.

If you have software mirror you can patch on primary disk by removing secondary and you can roll back server by secondary disk in case of any issue.

Hardware raid most of case hardware dependent.

You cannot swap disk from one server to another.

Chandra

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