Channels distribution

[Carlos Fernandez Riera]

Second way:

Unless you install PowerPath sofware, first way will use only one card.

On second all access is 'striped' over 4 cards.

[harry d brown jr]

If you can, you should first reduce the number of VG's you have. 20 VG's (or 20 LV's, because in your environment they are the same) at 32GB a piece is a lot to manage. There is no benefit to having 20 VG's/LV's. It actually increases your overhead.

Put all of the disks into one VG, then stripe your LV's across all of the disks in the single VG. Also, using a product like PowerPath might also sound very reasonable.

[Andre Da Silva Dias]

Strongly suggest the second way, you will load-balance between your four cards.
Also pay attention to the localization of your hypervolumes on the backend of the Symmetrix, unsure that they are not under the same disk director.

Regards,
Andr??

[Manel Ventura]

Hi Carlos,
thanks for your replay .

Yes, first way will use only one card, but it's just for the VolumeGroup vgsap1. For the VolumeGroup vgsap2 will use another card, and so on (I've got 20 VGs).

So, is it better to arrange each card for each VGs (first way) or arrange each card inside each VGs (second way)?

[James R. Ferguson]

Hi:

First, LVM does *not* load balance between alternate (pv) links. The primary path is used unless it fails, in which case the alternate link takes over. If you are using Veritas Volume Manager, then load-balancing does occur.

Assuming you are using LVM, I'd build my volume groups such that at least two, and no more, channels service each disk in a volume group.

Regards!

...JRF...



first allocate channels as the primary links to the greatest number of I'd setup paths so that you always have access to any physical disk by a least two paths. Then, I'd apportion channels to balance the four channels among the greatest number of physical volumes.

[James R. Ferguson]

Hi again:

Sorry, my post should read as follows, disregarding the verbiage after my signiture!:

First, LVM does *not* load balance between alternate (pv) links. The primary path is used unless it fails, in which case the alternate link takes over. If you are using Veritas Volume Manager, then load-balancing does occur.

Assuming you are using LVM, I'd build my volume groups such that at least two, and no more, channels service each disk in a volume group.

Regards!

...JRF...

[Andre Da Silva Dias]

Hi Manel,

I still prefer the second way, despite the load on the VG's, they will always be balanced through the stripes=pv-links.

Andr??

[Manel Ventura]

Hey guys, thank you for your help but I still have some doubts.

Andr??, I get four disks for each VG because those disks have a different Disk Directors each one. So I do stripe between them. Am I doing this correctly?

Harry, why having 20 VG's/LV's increases my overhead?

James, I agree with you. LVM does not load balance between alternate pvlinks, but I think you can use different primary path on different disks, and then, do a manual balance. Am I wrong? Why do you say that you'd build your volume groups such that at least two, and no more, channels service each disk in a volume group?

[harry d brown jr · Accepted solution]

From what I remember each VG has a memory requirement of around 400kb.

In your environment, you have 80 disks, with groups of 4 belonging to a VG/LV. If you were to create fewer VG's, you could stripe across more disks. As an example, lets say one VG. That would mean that every disk would have 100 extents per LV (assuming 4mb PE's), so that no more than 400mb per disk per LV.

Of course any way you do it, without something like powerpath, you will have to manually do the alternate pathing. Not usually a big deal, especially if you know how to cut/paste and write scripts.

harry

live free or die

[James R. Ferguson]

Hi Manel:

I was needlessly confusing in my first reply. By all means choose your second scheme. Not only does it offer high-availability should any primary channel fail, but it balances channel utilization too.

I also agree with Harry. Reducing the overall number of volume groups and increasing the number of physical disk in each allows any given logical volume to be stripped across more disks, potentially further improving performance.

Regards!

...JRF...