mirrordisk and sc10 array

[Mark Greene_1]

We have and sc10 array with ten 18.2gig drives setup in 5 RAID 1 pairs using mirrordisk. I want to swap one pair out for a pair of 36.4 gig drives to get more space. I have two questions:

- will both the sc10 array and the mirrordisk software play well with the mixed drive sizes?

- it appears the mirrordisk consumed almost 1gig on each drive (sam reports them as 17.3 gig). is this normal?

- does hp have a whitepaper on mirrordisk? I did a search but could not find one

thanks
mark

[Helen French]

Hi,

This document will give you an idea about Mirroring using LVM:

http://www.docs.hp.com/hpux/onlinedocs/B2355-90672/B2355-90672.html

Shiju

[Mark van Hassel · Accepted solution]

You should not have any problems unless the the Maximum number of PE per PV (see vgdisplay -v [vgname] )is lower than the new disks are capable of. This means that you can only use the that nr of PEs of your disks and the other space cannot be used. The only solution is to backup your data, create a new vg and restore your data.

If this is not the case, do as follows:

For each lvol in the vg:
lvreduce -m 0 [lvol name] [diskname]

Then remove the first disk from the vg:

vgreduce [vgname] [diskname]

Add the new disk to the vg:

pvcreate [newdiskname]
vgextend [vgname] [newdiskname]

recreate the mirrors for each lvol:

lvextend -m 1 [lvolname] [newdiskname]


After this do the same for the second old disk and second new disk.

Good luck,

Mark

[Tim D Fulford]

Mark

As far as the SC10 is concerned I think the disks rae hot swappable.

However, you will have problems with LVM. Even though the disks are twice as large you probably will not be able to see the extra as the volume group was set up wityh 18GB disks.

However, If the disks you want to swap out are a mirrored pair and no LV's are shared with other disks (e.g. extent based stripes, etc).
o replace each disk one at a time so the mirroring can take place. check for stale extents with pvdisplay.
o vgreduce one of the mirrored pairs. Then create a new VG & put it in there.
o create the LV's in the new VG with the same sizes as on the old disk LV's.
o Stop all you apps using the LV that will be effected. copy the contents of the old to new LV's dd if=/dev/vgold/lvolXX bs=1024k of=/dev/vgnew/lvolXX
o edit /etc/fstab (if req) to point at new VG/LV
o start up apps
o Finally lvremove the old LV's & vgreduce the old disk out. pvcreate it & add into the new VG. mirror up.
DONE

If you use extent based striping, you are stuffed for a quick fix. You'll need to recreate the whole volume group from scratch.
o stop apps
o level 0 of all the VG's filesystems & databases
o save VG size & config info, vgdisplay -v
o vgexport vgold
o pvcreate all the disks
o vgcreate/vgextend all the disks onto the new VG. It will probably change some of the default VG parameters like "MAX PE per PV" or you may need to increase "PE Size" to 8MB
o restore info
o start up apps

Both of the above should be done with all the applications stopped at some point, it may be possible to get 'round this by using "your skill & judjement".

Tim

[Helen French]

Hi,

Again, while you mirror the disks, if you have two controllers in the SC10, then configure the mirror with seperate controllers. That means two disks in the same controller and the mirror disks in the other.

Becuase, if you have 2 cotrollers, you can access all HDD with two different links ( check the full-bus/split-bus configuration). And this will improve the performance too.

HTH,
Shiju