Adding disk to EVA / volume group

[Mike Tufariello]

Briefly, I have a volume group with an lvol that needs at least 50 GB of space added to the lvol. The volume group is made up of 9 virtual disks of 50 GB each, from a disk group on my EVA of all 36 GB, 15K, drives, operating in a RAID 1 protection. So I am assuming this disk group needs to be expanded.

The way I understand EVA "best practices" I could add a minimum of 8 more 36 GB, 15 K drives to the disk group. (This will only realize 4 drives due to RAID 1 protection.)

How I need help;

1) Is this the correct approach?
2) Can I mix higher capacity drives (72 GB or 144 GB) with the 32 GB disk group instead?
3) Would it be cheaper to use remarketed 32 GB drives instead of new 72 or 144 GB drives?
3) what are the steps that permit the EVA to see the new drives?
4) what are the steps to create the new virtual disks?
5) what are the steps to add the virtual disks to the volume group?

Thanks very much,

[Steven E. Protter]

Shalom,

You may have a problem that you have not forseen up to this point. The existing volume group was probably not created with enough free, distributable PE's to accommodate the massive infusion of space you are planning.

You will need to back up all the data on the existing volume group, and re-create it with the vgcreate command. This is very,very likely.

Use the -p parameter when using the vgcreate command. Set the number of physicals to a reasonable leve, but not the default which is 255.

Now to your questions:

1) Depends on your needs. If you need more space longer term, go with larger capacity drives. The performance hit depends on configuration more than drive size.
2) You can mix drives. The Volume group cares about available physical extents, not the composition of the LUNS.
3)Plug in drives.
4)Configure drives into a LUN on the EVA utility, which is on a Windows control station. Assign the disks to the already created LUN.
5)Reboot the system after the LUN is expanded, lvextend, extendfs or faadm (only if you have Online JFS).

SEP

[Mike Tufariello]

SEP,

Shalom,

Here is my vgdisplay of the volume group. How can I tell if I have enough PE's to accomplish this?

VG Name /dev/vgprod1
VG Write Access read/write
VG Status available
Max LV 255
Cur LV 11
Open LV 11
Max PV 16
Cur PV 9
Act PV 9
Max PE per PV 12799
VGDA 18
PE Size (Mbytes) 4
Total PE 115173
Alloc PE 112948
Free PE 2225
Total PVG 0
Total Spare PVs 0
Total Spare PVs in use 0

Thanks,

[Dave Hutton]

If you have open slots in any of your enclosures you can populate those. If you are out of slots you can add more enclosures.

You can add just 1, but my understanding is 2 enclosures are better and best is 8 enclosures due to how the RSS grouping happens.

You don't have to at them in 8's. You can add just 1 if you wanted to. But depending on how your rss groups are set up 8's may keep your enclosures better aligned.

2) You can mix 72, 146 or 300 gig drives in the same disk group. Since 300 gig drives are more dense they may do a little extra work. From my understanding not noticable. If you were to do two 146's instead of 1 300 obviously you have 2 physical disks that can offload onto each other.

3) No idea, guessing they could be cheaper.
3a) Like said above, just pop them in. Usually if you do a bunch of disks you don't want to group them all at once. I've done that and was told not to do it again, it caused a lot of grey hairs and some sleepless nights. Usually you pop them all in. It'll show up in the ungrouped pool. Add in 1 and watch data go to that disk til you have a few gigs on there. Then group the next one and so on. There is a button to group all, but if you have 2 faulty disks in the same rss group you could have some real issues.

4) Just use commandview EVA, its pretty easy. Being you already have disks out there presented to this host it should be pretty easy to see. Just create new vdisk, tell it the size and your raiding. Tell it what host to present it to and select failover path A or B. You want to alternate these since they will use the opposite controller to do its work.

5) Theres a bunch of searchable suggestions on how to add disks into a vg. But you basically present the disks, insf -Cdisk, vgextend the vg and then lvextend (or lvcreate if you want new ones).