VxVM & ServiceGuard

[Duncan Edmonstone]

Anyone come across this (purely theoretical) situation:

MC/ServiceGuard Cluster with shared FC10 disks (or in fact any type of JBOD disk system)

If I wanted to use VxVM with ServiceGuard I have a number of issues:

1. I can't use a VxVM disk for the cluster lock, so I lose one entire disk which has to be under LVM control.

2. VxVM requires a 'rootdg' on both nodes in my cluster, but 'officially' Veritas don't support 'data' in the rootdg, its supposed to be for the OS only (except it can't be on UX11 or 11i - only on 11i 1.5 or 1.6) - so I have to dedicate a whole empty disk *again* to the rootdg.

3. What happens if the rootdg on either node fails? Well as I understand it, at the very least you will be unable to change anything in the VxVM configuration, and in fact VxVM could pack up completely! So for proper availability I should in fact mirror my rootdg - thats another disk!

So in a two node cluster I have five disks that I can't use as part of my shared storage! Thats terrible -on a FC10 with typically 36GB disks thats 180GB possibly wasted! Or am I missing something?

If I have a RAID disk array of some kind, then obviously this isn't a problem - I can just set up small 10MB luns to cover this off. Otherwise... JBODs / ServiceGuard and VxVM just don't seem to mix very well.

[Duncan Edmonstone]

Ping!

[Pete Randall]

Duncan,

I was going to reply earlier but all I could think of to say was that you're right. I don't think Veritas was thinking about this sort of scenario.

Pete

[Martin Johnson]

Veritas has its own clustering product. Have you look at it as an alternative to ServiceGuard?


HTH
Marty

[linuxfan · Accepted solution]

Hi Duncan,

1. Yes you loose an entire disk. You can probably get by using quorum server in a non-production environment.

2. rootdg can have non-OS related/non-shared data (as mentioned in the VxVM migration guide, but yes in our case it was wastage of disk space.

3. Additional Cost. At this point it is obvious we need to have LVM, Mirror/Disk-UX . On top of this if you need to mirror you VxVM disks, you need to buy additional licenses.

On top of this, there are lot of other "factors" that you need to consider if you have an existing cluster and need to migrate it to VxVM.(Downtime for sure). Not sure how smoothly rolling upgrades go with the migration.

/quote from the migration guide/
The conversion process does not support conversion of any volume group that is marked as a member of a MC/ServiceGuard or OPS Edition high availability cluster. The volume group must be deactivated and removed from membership in the high availability cluster before it can be converted.

/quote/

Actually if you are using diskfarms(EMC/XP256), then you can probably get by allocating more disks. but as you mentioned, if you are using FC10 arrays or autoraids /JBODs(limited number of disks) then you are wasting disks. Worse, if you are using Autoraid, then you hit the limit of 8 LUNS pretty fast.

Yes, you pretty much summed it up very well, MC/SG and VxVM don't mix very well, atleast at this point of time.

-Ramesh

[Duncan Edmonstone]

Thanks for the input guys, looks like this is a non-starter then...

Pete - Absolutely -I guess with VCS being a direct competitor for MCSG, they have no good reason to think about this type of scenario...

Martin - yes I am familiar with VCS - a good product which has the same cons as all other Veritas produts - its so damned expensive! In the particular scenario I had, VCS wasn't an option anyway...

Ramesh - thanks, you confirmed my suspicions -it would be nice to hear if these issues will be addressed in future versions of MCSG/VxVM

The reason I was interested in using VxVM was so I could then use Veritas Volume Replicator - we have a requirement to replicate a ServiceGuard'd application to another site using only IP links, and we didn't want to have to use hardware replication like XP CA or EMC SRDF - its a shame there isn't an IP based volume replication product for LVM...

Cheers

Duncan

[Amruth]

Hi,

I am also in a similar kind of Situation.

We have XP1024 and 2 V-class servers.....and Veritas....

Regards,
AR