[SunHELP] more on mirroring

[Dale Ghent]

On Wed, 24 Jan 2001, Tom Lieuallen wrote:

| 
| I saw the question and answers about mirroring in the last digest.
| I'm assuming that by having two disk bays and selling two disks
| with the 220 and 420's was so that people could and would mirror
| the boot disk.
| 
| But, from my perusal of the disksuite instructions on mirroring,
| I'm not sure what the recommended setup would be.
| 
| The problem I have is with the metadb's.  If you only have two
| disks, then they recommend putting at least two metadb's on each
| disk.  If one disk fails, it can continue to run with half of the
| databases.  However, if I read correctly, at boot time, it has to have
| half plus one or it won't boot.

Not in my experience. You can have two disks, and metadb on both. If one
becomes unavailable (taking half your metadb copies), the system will
still boot on the metadevice. SDS knows that additional copies
should be on that disk, but since they're unavailable, it uses what it has
(and you'll see the failed disk noted when you run metastat).

The SDS driver keeps tabs of it's metadb locations by entries the metadb
utility maintains in /etc/system.

So getting a 220R/420R with two disks and mirroring the partitions on
those disks is fine. I do the same thing here at home, albeit on a Ultra
2, but it works great nonetheless when I yank a drive out to test it.

/dale