AIX

We have an IBM pseries with AIX 5.1 that we are going to set up with RAID 5. It has a 7028-2498 RAID controller that was never configured, long story. It has six 36GB drives, and my question is, can we set up the RAID 5 array before reloading AIX, such that all six drives are part of the array?

I don't understand what reloading means.
Is your AIX on separate disks or on one of those 6 drives connected to the raid controller? Maybe you give a bit more detail.
We have some old DPT RAID controller and if I recall correct, it deleted existing data on disks, if you chose to build a new array. Maybe check the doku for your controller.

Thanks for responding. AIX is currently loaded on disk0. Since this server was never configured with any RAID settings, but has years of data written to the other disks, we are going to copy the data out, and reload AIX with the array configured for RAID5. It looks like the typical approach would be to reload AIX on disk0, mirror it with disk1, and use the other four disks for the array. My question is, can the array be setup before AIX is reloaded, such that we can use all six drives in the array?

Now, that it becomes clearer what ou want to do, i'd strongly suggest you dont do that. Keep in mind that to create a RAID from several disks is not only a feat the controller does but also the accompaning driver layer. This means that the machine would have to boot from a device which only comes into existence due to the work of a loadable piece of software (the driver) which is stored on the device it tries to make function - a circulus vitiosus, so to say.

Therefore i doubt that it is even possible to boot from a RAID device, but even if it is - don't do it and spare yourself some nightmare. Consider the following, not too farfetched situation: you upgrade the system and upgrade the driver software, which in turn makes the RAID unmountable for some or other software glitch. There is a BIG difference between having a system, which runs but is unable to mount its data storage and a system which is completely unbootable because the most core FSes won't mount, in fact even the kernel image cannot be loaded.

Do yourself a favour and make two disks a mirror, where the system software resides (rootvg) and the other four disks use as a RAID array.

I hope this helps.

bakunin

O.k., so you make an excellent and well taken point. Last question, is there any issue if I keep the 36GB drives disk0 and disk1 for mirroring the OS, and replace the other four 36GB drives with 73GB drives?

No, not at all. First identify carefully which physical disks are "hdisk0" and "hdisk1" (have a look at the location codes). Then install AIX on one of these disks, add the second one to the rootvg and run "mirrorvg", which will mirror every FS in the volume group. Replace now (or before, it doesn't matter) the other four disks, create a RAID array from the new ones and create a volume group from the disk device the RAID controller has created. Check with "lspv", hdisk0 and hdisk1 should belong to "rootvg", all the other disks to "datavg" (or whatever you name it).

Now create LVs/FSs from the datavg and fill with data, etc. (probably you will simply have to restore it from somewhere).

If you want to replace the disks of this datavg you can do so by "varyoffvg" the datavg. You could work on these disks without even shutting down the machine (another advantage of having the OS software separated from the data).

I hope this helps.

bakunin

Great, I think we will proceed as you describe. Forums like this are probably the most useful thing the Internet has to offer from my perspective. Thanks alot for sharing your expertise.