topic Re: Sharing LUNs on va7400 ?? in Disk Enclosures

Sharing LUNs on va7400 ??

Bill Costigan — Thu, 28 Mar 2002 16:15:18 GMT

I'm looking for some help.

I have a client, who thinks they would like to mount the same LUN on two different HP-UX systems. R/W on one system and R/O on the other.

I'm not even sure this can be done. But I'm pretty sure it's not a good idea. I see all kinds of problems with the R/O system trying to figure out what's happening while the R/W system is updating data and inodes.

I'm going to recommend either a snapshot LUN using business copy or simply NFS mounting the file system.

But before I do, I wanted to see if anyone had any other thoughts.

Thanks

Re: Sharing LUNs on va7400 ??

David Bell_1 — Thu, 28 Mar 2002 16:24:18 GMT

Bill,

I think your thoughts are right on the mark. I would do a BC or NFS.

Dave

Re: Sharing LUNs on va7400 ??

Steven Gillard_2 — Thu, 28 Mar 2002 17:31:48 GMT

It is possible, by activating the volume group that the LUN is part of in read-only mode. The 'WARNINGS' section of the vgchange man page has a good discussion on this:

"In ordinary operation (i.e., without the optional high availability software), it is possible to activate a volume group for read-write access from more than one physically connected system, leading to a high potential for data corruption. Therefore, if access is desired from more than one system to a single volume group, it is important that only one system activate the volume group for read-write access; the other systems can use read-only access. There is no problem if all systems activate the volume group for read-only access.

Furthermore, volume group information is only read from the disks during volume group activation. Dynamic changes to the volume group such as the following are not propagated to other systems sharing the volume group:

Logical volume configuration changes.
Changes to the status of the mirrored extents.
Bad-block relocation that occurs during write operations.

Because of these limitations, when sharing volume groups between systems it is recommended that logical volumes be accessed only by one system at a time. If logical volumes need to be accessed simultaneously, the logical volumes should not be mirrored and should not have bad-block relocation turned on, or all systems should use read-only access to the logical volumes."

Regards,
Steve

Re: Sharing LUNs on va7400 ??

Vincent Fleming — Thu, 04 Apr 2002 18:25:37 GMT

You want Veritas File Sharing Option.

See http://eval.veritas.com/downloads/pro/fso_hp-ux_datasheet.pdf

for some details.

Basically, you can mount a FS R/O by one system, and this software "ie: hack" keeps the R/O system from crashing when the R/W system updates the FS. (it eliminates inode and directory caching, among other things)

Good luck!

Re: Sharing LUNs on va7400 ??

Vincent Fleming — Thu, 04 Apr 2002 18:32:56 GMT

Oh, by the way, FSO is available ONLY for HP-UX...

Nice, eh?

Re: Sharing LUNs on va7400 ??

Bill Costigan — Thu, 04 Apr 2002 18:40:47 GMT

Thanks Vincent. I had no idea that existed.