Mirror Disk Question

[ROSS HANSON]

I had to add a disk to vg00 to increase the size of /home
Do I now have to break my mirror and remirror again?

[James R. Ferguson]

Hi Ross:

No, you do not need to break the mirror. Just resize the filesystem (on-the-fly if you have Online JFS).

...JRF...

[James A. Donovan]

How much you can extend your /home filesystem will probably depend on how many free extents are left on the disk you mirror with. Since you've only added one disk, not two, and by default the allocation policy is to place mirrors on seperate physical disks, I'd say you're probably not going to be able to extend /home very much without making a couple of changes.

How many disks were in /dev/vg00 originally? What is the allocation policy on the /home logical volume? (lvdisplay /dev/vg00/lvol?, look at the "Allocation" line.)

You'll need to do a little digging on your end, but I suspect that to increase your /home, you'll need to run:

# lvchange -s n /dev/vg00/lvol5

or else break the mirror.

One last thought, you should seriously consider adding drives in pairs when you have a mirrored environment.

[Tim Malnati]

There are some methods available to handle the physical mirror locations that Jim Donovan mentioned. You do this by moving the mirrors around. The Mirrordisk product allows you to have up to three images of a file system. This allows you to create am additional mirror of an existing file system on the new disk prior to removing it from one of the existing drives while stiil maintaing the 'strict' policy. You need to use the lvextend and lvreduce command manually using the physical disk parameter to designate where to put it and where to take it away. If all your drives on the same bus there is little difference to the system. But if your drives are on separate scsi channels and the new drive has been added to one of them you could end up with data traffic issues. In this situation the best filesystems to have two mirrors on the same channel are those that do not get accessed very much. Also, it is not a good idea to move /, /stand, and swap from the initial two drives where they are needed for booting; having these file systems on the same drive as the lif is best. Now all of this problem could be eliminated by adding two disk as Jim suggested.