Reading meta data of the HP-X LVM physical volume.

[PrasannaKumari]

1)Is it safe to read the meta data of the LVM physical volume? I am opening the LVM physical volume device file and reading the PVID of it using the read call. I have a the code written in C which is being invoked from java i.e a JNI call.

2)If reading the physical volume is safe enough, should we be opening a raw device file or a block device file for reading? Does this have anything to do with the utilization of CPU especially if the HP-UX host is having a number of LVM physical volumes?
The LVM physical volumes have oracle database installed on them through a file system.

[Bill Hassell]

The LVM data is just raw data on the volume and reading the track with the PVID is just a simple read. You always open the raw device file when reading raw data. The block device is reserved for mounted filesystems so the driver can take advantage of the buffer cache.

As far as a load, if you are just gathering the PVID for each disk, reading 1 track from 500 disks is not significant. Running bdf on a system with 200 mountpoints is a 100x bigger load. And in either case, you would only run this read once in a while.