topic Re: Can we mount a device on more than one machine at a time ? in Operating System - HP-UX

Can we mount a device on more than one machine at a time ?

Masthan — Fri, 28 Sep 2007 00:12:59 GMT

Hi All,

On any operating system(unix/linux/solaris), if a device is shared by more than one machine, Can we mount that device on all the machines?

If so how? if not why ?

Re: Can we mount a device on more than one machine at a time ?

Torsten. — Fri, 28 Sep 2007 00:38:06 GMT

It depends on the file system used.

Some file systems are able to be shared between several machines - some not.

The problem is, if you share a file system that is not able to do this, one host will modify the file system while another is doing the same without any knowledge about this - you will have a perfectly corrupted system then.

Possible workarounds are read-only mounts or nfs.

Re: Can we mount a device on more than one machine at a time ?

Yogeeraj_1 — Fri, 28 Sep 2007 06:30:31 GMT

hi,

Using NFS you can mount the same share (as defined in your /etc/exports) on several machines. This is quite easy to implement. see "man nfs" and "man exports"

hope this helps!

kind regards
yogeeraj

Re: Can we mount a device on more than one machine at a time ?

Steven E. Protter — Fri, 28 Sep 2007 06:38:07 GMT

Shalom,

NFS does seem to be the best tool for the job.

The machine acting as NFS server will have to access the file locally, but this will work.

SEP

Re: Can we mount a device on more than one machine at a time ?

Torsten. — Fri, 28 Sep 2007 06:42:02 GMT

Your profile says:
I have assigned points to 0 of 49 responses to my questions.

Please read
http://forums1.itrc.hp.com/service/forums/helptips.do?#33

Re: Can we mount a device on more than one machine at a time ?

A. Clay Stephenson — Fri, 28 Sep 2007 09:59:09 GMT

Veritas makes an extension to its vxfs filesystem called the Clustered File System which does just what you want and is available for a number of platforms. This CFS product is available directly from HP.

The problem with trying to mount the same filesystem on multiple hosts is buffer cache consistency. Normally server A won't have a clue about what is in server B's buffer cache and absolute chaos is assured. CFS maintains a link between all hosts so that the filesystem appears to be a local vxfs filesystem on all hosts.

Now, it is possible to "mount" raw devices on multiple hosts and since raw devices bypass the buffer cache, it is possible for these to read and write to the same device from multiple host but the software must handle device contention itself. In addition to disk devices, tape devices can be shared among multiple hosts.

Re: Can we mount a device on more than one machine at a time ?

Geoff Wild — Fri, 28 Sep 2007 10:14:15 GMT

Yes it is possible - either via NFS or Cluster File System.

Course, with CFS, you need ServiceGuard:

http://docs.hp.com/en/T1859-90048/ch03s11.html

Rgds...Geoff

Re: Can we mount a device on more than one machine at a time ?

Jan van den Ende — Fri, 28 Sep 2007 11:30:21 GMT

Masthan,

>>>
On any operating system ...
<<<

Well, if you are willing to include OpenVMS in your definition of "any", then that is your answer.

In VMS (as it is still called by its afficionados) that is the normal behavior.
Always. In any access mode. The systems can be VAX, Alpha, and Itanium, or emulations on X86 or X84-64. Simultaniously. Officially supported up to 96 systems maximum, the number for unsupported but functioning configs gets wat into 3 digits.

hth

Proost.

Have one on me.

jpe