What will happen to ASM when the disk path changes in Linux?

Posted by David Yahalom under Storage, ASM, RAC, Oracle

Have you even wondered what happens if disk device names and/or major-minor numbers changes at the operating system level? Will this cause any problems for ASM as it tires to access the drives even when the drive path has changed?

Well, no ! This will cause absolutely no problem what so ever to ASM. In fact, its one of ASMs best features.

You see, ASM only cares about the LOGICAL disk names and not the PHYSICAL drive paths or numbers. Changing the drive paths or major-minor numbers in the O/S is no problem for ASM. This is because ASM scans the disks based on what is defined in asm_diskstring - so during boot, all drives that have a valid ASM header will be automatically added to ASM.

These devices are opened with system calls (like fopen, etc.) so paths and/or major numbers are not even used.

The disk paths, names and major-minor numbers are not persistently recorded in any of the ASM metadata. Each ASM disk has a disk header which contains the disk name and diskgroup stamped in it.

If ASM discovery finds the required number of disks for a given diskgroup then it will be able to mount the diskgroup. The ASM metadata header will contain the fixed and persistent logical disk name (for example - ORCL_DATA_DISK1). On boot, ASM will scan all disks for one with the above name in its header.

Once it finds that disk it will make the connection between the current (again, not persistent) disk path and the logical disk name.