topic Re: Adding a disk array and mirror disk to an A class in Disk Enclosures

Adding a disk array and mirror disk to an A class

Mark McDonald — Wed, 29 Oct 2003 07:49:43 GMT

Hi

We have an A class machine with 2x 18gb internal disks. 1 for the unix and 1 for the application. I have been tasked with getting these disks mirrored.

I am familiar with MirrorUX software, but need some advice on the best way to add more disks to the system.

Can i simply add an SC10 or something similar? can i just mirror the internal disks on to this? Or would it be better to have root and root mirror internal and application and application mirror external?

Thanks

Mark McDonald

Re: Adding a disk array and mirror disk to an A class

Mark Grant — Wed, 29 Oct 2003 08:00:26 GMT

It is better mirror root and boot internally and the applications externally (if they don't fit on the same disk).

This is mainly because the most likely disk subsystem to be available during boot is the internal disks. You should make the mirror bootable as well so that if your root disk fails on boot, you can still get a system up and running..

Don't forget to mirror swap! I've seen that happen before and watched applications fall over when a supposedly mirrored disk failed.

Re: Adding a disk array and mirror disk to an A class

Mark McDonald — Wed, 29 Oct 2003 08:12:05 GMT

Thanks Mark

I have just been speaking to a colleague about this. He seems to think that mirroring the root internally is better for protecting against disk failure, but keeping the mirroring external will protect against scsi controller fialure too.

Does the external scsi interface on the A class use a separate controller?

Re: Adding a disk array and mirror disk to an A class

Mark Grant — Wed, 29 Oct 2003 09:16:58 GMT

I think it uses the same controller anyway but even if it didn't then you wouldn't be able to boot after losing the root disk if you haven't made the external disk bootable. Making the external mirror bootable is not only a pain but they may well not even exist during the inital boot process.