Is it possible to share vg without service guard?

[Mauro Gatti]

Hi all,
Is is possible share a volume group between two hosts without service guard?
I need two create two logical volumes mirrored belonging to a same volume group that have to be visible from two host. I don't need any file systems on these LV and any concurrency check because it will be made by another software.

I read that is impossible create shareble vg lv mirrored without service guard. Isnt' it?

Thank You

[Geoff Wild]

I don't see why not...they just can't see it at the same time.

Build the vg/lvs on one host.

vgexport -p -s -v -m /tmp/vgXX.map
vgchange -a n /dev/vgXX

On 2nd host:
mkdir /dev/vgXX
mknod /dev/vgXX/group c 64 0xHH0000

(where XX is vg number and HH is hex of minor number).
Then vgchange -a y /dev/vgXX

On both hosts set
AUTO_VG_ACTIVATE=0
in /etc/lvmrc

In the custom_vg_activation() section, add only those vgs you want activated.

Rgds...Geoff

[TwoProc]

As long as you know when each one is defined and connected and your software takes care of concurrency issues for you (if they are both connected - raw disk only), then no problem. That's how Oracle RAC works by the way, so no big deal. Just know that HPUX at current time is not a clustered file system that can share file systems- but it can share devices.

[Pete Randall]

Actually, despite what the man pages say, this can be done. It does have a substantial share of risk, though. You have to ensure that only one system has write access or you're going to have a disaster on your hands (I know, believe me!).


Pete

[Kent Ostby]

Mauro --

One of the things that ServiceGuard buys you is a different set of software that includes something called slvm which is "shareable" lvm which has special features.

While I suppose it could be possible to do raw I/O this way, you wont be in a supported configuration from an HP point of view.

The other possibility might be to install the ServiceGuard software to get the slvm but then run your application outside of Serviceguard.

Best regards,

Kent M. Ostby

[Leif Halvarsson_2]

Hi,

If you don't need any filesystem it is perhaps easier to use the physical disk direct (the raw devicefile). In a SAN enviroment this is rather easy, just create a LUn, present (or zone) it to both hosts and then , create devicefiles on both hosts.

[Gordon Morrison]

If this is not going to be a raw volume, then make absolutely sure that it is not directly mounted on more than 1 host unless it is mounted read-only on ALL of them. Otherwise filesystem corruption will almost certainly result.

Mounting it read-only on several servers is safe.

Mounting it read-write on 1 server, and NFS mounting it on several other servers is safe.

Mounting it read-write on one server and read-only on another will *_at best_* give the read-only server bad/obsolete information about what is on the filesystem, as it won't be looking for updates that may have been done by the other host. (Why should it? It's mounted read-only, right?)

Only mount it read-write on more than one server if you are seriously considering a change of career:o)

[Mauro Gatti]

In effect I would want put on it OCR and Voting structures of oracle 10g and I also would want thay are mirrored.
If I used raw disk I would use 4 disks (2 for OCR and 2 for voting) and I would need a RAID controller on my servers.
So I thinked to take two disks, to include them in a new VG, to create 2 LV mirrored: one for OCR and one for voting and then to give to oracle rlvol special file to be used as it needs.
Do you think it is possibile?

[Leif Halvarsson_2]

Hi,
Why do you want to use mirroring together with hardware RAID. Unless the mirrors is on separate LUNs and the LUNs on separate RAID-sets (or disk groups) it will not give any petter security, only performance overhead.

[Mauro Gatti]

Leif, I don't want use mirror together RAID.
I would want to use lv mirror instead of RAID card but I didn't know if I could create shared VG (visible in the same thime from two hosts) without service guard (because oracle would use raw special LV file and would control concurrency)

[Leif Halvarsson_2]

Hi
Sorry, I misunderstood you .

[Gordon Morrison · Accepted solution]

You may want to check out this thread:
http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=821953