mirrored LV's ???

[MikeL_4]

I have six (6) disk within an Volume Group with three (3) being down path: c1t.d. and the others down path: c2t.d.

Is there a way to make the c1t.d. path the primary path and the other the secondary ??

Thanks
Mike

[erics_1]

Mike,

Sure. Just specify the disks you wish to be the primarys when creating the lvols. You can specify which disks you wish to have as the mirrors as well if not all 3 primary disks are being used yet. Take a look at Knowledge Base Document # ULVMKBRC00008267
How to mirror logical volumes to specific disks

Best Regards,
Eric

[Patrick Wallek]

There really is no "primary" and "secondary" regarding mirroring. When something needs to be written to a filesystem that is mirrored the write will be done on both disks and if something needs to be read, the disk with the quickest response will be used.

If you have a failure, the other disk in the mirror will be used until the bad disk is replaced.

[Rammig Claus]

Hi Mike,

pvchange -s
But this is only temporary.

If you want this permanent, you had to reduce and then extend the volumegroup.

lvreduce vg...
-> the alternate path is now your primary

lvextend vg...
-> the extendet disk is now the alternate


Best regards ..
Claus

[Vince Inman]

PV links does just that by default. The lower controller number (c1) will always be the "primary" path to a device, with the higher controller path being the "secondary".

You can change the primary path to a device but upon reboot, it will revert to the lower controller first.

In actuality, if your description is correct, you really only have three disks in your VG with two paths to those disks, as opposed to having "6" disks.

[MikeL_4]

Thanks Eric

In this case it is an inharited system and the LV's are already defined and in production. Does the lvdisplay show them in primary/secondary order ??

Thanks

[MikeL_4]

Thanks All

This explains alot for me, thanks for your quick responces.

[erics_1]

Mike,

If you run an lvdisplay -v on your lvol, you'll see towards the bottom that the primary extent locations are listed on the left side while the corresponding mirrored extents are on the right. Sorry, I didn't realize that the lvol's had been created already.

Eric

[Dave Wherry]

Vince,
He's asking about mirroring, not alternate links. There is a primary and a secondary.
Could you explain a little more? I've never seen the behavior you talk about. Reverting to the lowest numbered controller on a reboot. I've had systems with a primary and up to 3 alternate paths and have never had the order change on me unless I reduced and extended them.

[Jean-Louis Phelix]

Hi,

In fact it's quite simple : you really have a primary and a secondary, but the order of the disk at lvol creation doesn't really matter. It's only used until you deactivate the vg (don't even need a reboot to loose it). When you reactivate the vg, the first disk found in lvmtab will be used as primary, the second as secondary. The same rule applies also for alternate links. Only the order of the disk in /etc/lvmtab is important.

Regards.