vxvm : dg size and recommendations

[posie80]

Hi all,

I have a pretty basic question to you experts :

Is there a recommended dg size that should be followed when creating dgs? I read that excessively large dgs can cause private regions to fill up pretty quickly, but I dont know how big is 'excessive'. Is  a 800 DG diskgroup considered big?

Also, is there any benefit in creating multiple dgs instead of just one big one (if all the volumes inside the dgs have the same specs/need).

Thanks and appreciate your feedbacks!

- Posie

[ScottK · Accepted solution]

The number of disks in the dg has much more impact than the size of the disks in filling up the private region metadata. If the 800GB dg is 800 LUNs * 1 GB/LUN, then you have used a lot of private region space. If the 800GB dg is 1 LUN * 800GB/LUN, you have used very little.

I have an 8TB dg comprised of 16 LUNs. Plenty of private region space left.

One of the main benefits of a dg is as a handle to move a whole bunch of related objects around; for example when failing over in a cluster, or during a migration. I try and group an application within the same dg.

[Gaurav_S]

Thats right, number of objects would matter & not the size.

As Scott mentioned, there could be number of subdisks /plex / volumes/ subvolumes / snaps which may fill up your private region space..

One thing which I would stronly recommend to check here is the version of volume manager. In earlier versions the default private region space was was pretty less. Starting 5.x it was increased to 64K I believe which could incorporate lot many objects. I hope you are using 5.x

Gaurav