AIX

Hi all,
I'm just wondering here....
When we're talking about mirrorvg and it's siblings we're talking about software raid...
right ?

In fact we are talking about "disk mirroring" or "disk duplexing" by software means. Usually we call only a RAID-5 a "RAID". So in a broader sense, including RAID-1, yes we are talking about software RAIDs.

I hope this helps.

bakunin

Thanks for the reply
The reason I asked is that we're about to purchase 8 new p-series servers and I've had a bad experience with our older p-series servers. When a disk failed in the rootvg the server became extremely busy trying to correct the problem which resulted in a software crash.
Hopefully if the disks is handled by a RAID controller this will not be a problem.

As long as you maintain a correctly mirrored rootvg an AIX server will not run into deep trouble when one disk fails. That a server becomes "extremely busy" after a disk went missing sounds like the server was trying to find information that was not on the remaining disk.
So for reasons of safe operation there is rarely a need for a physical raid adapter. If you are new to AIX and unsure about how to use mirroring, you might use the mirrorvg command to mirror your rootvg. This has the advantage over mklvcopy that one cannot forget to mirror the boot device hd5 or the paging space.
When you add an LV later make sure that you tell LVM to create 2 copies (default is just 1 - even if the VG is mirrored already, leaving you with a partly mirrored VG) and place each copy on a separate disk. This way you will hardly run into dire straits when a disk goes missing.

I'm not talking about a minute or more of extreme business, just enough that the software running on the server felt starved of resources and decided to exit.... And yes I'm sure that the mirror was correctly set up.

But it's kind of a mute point since I've heard what a dedicated hardware raid on p-series server costs.... approx. $3000.... which is kinda LOT

We have all our server's OS on AIX mirrored rootvgs and use no extra hardware raid controllers for that. Whenever one disk failed, we had no noticable breakin of performance iirc.

Maybe setup a test server and use something like nstress to simulate traffic and pull one of the mirrored disks and see if it still handles anything according to your needs.

Edit:
Maybe you have LVs in your rootvg that contain data or database stuff etc. ie. which you might move to SAN storage so you will not have such bad performance when one disk fails.

Thanks
I didn't know about nstress....I'll give it a try