Is there any way we can mount a file system on top of a mirrored/replicated volume? I am ok with having a read only filesystem on top of the mirrored volume, as long as the filesystem reacts to changes to the data in volume on top of which it is mounted.

Hi

I'm not sure if I understand the question, but it sounds like a mount with the --bind option. You can mount using for example:

mount --bind /path/to/the/mounted/volume /path/to/a/new/directory

If you want it to be read-only, you can add "-o ro" to the mount command.

See "man mount" for some more information.

Doesn't make any sense - the filesystem is the data to all intents.
The application talks to the filesystem - the VFS layer hides all the details; what happens below that is irrelevant (but useful). Could be RAID, could be mirrored - might be striped LVM on (hardware or software) RAID on a mirrored set. Yes, I know you wouldn't do that - but you could.

If the mirrored/replicated volume is on a separate system and the volume
is receiving updates from the volume on another system, then you do not
want to mount a file system on the mirrored/replicated volume.
The reason is that the replication is done on the block level, the file
system on the top has no knowledge of what the replicated volume will
contains after mounting as it continues to be replicated and updated
by another volume. The following FAQ page about DRBD is an example,
"Can I mount the secondary at least readonly?"


http://linux-ha.org/DRBD/FAQ#head-2c...95390c742ebd86

This problems exists on every block level replication products like
disk replication(DRBD), storage replication, volume replication
implemented on either software or hardware.

You can mount the mirrored/replicated volume safely only after the
replication is stopped due to remote system's failure or being shutdown.
The system may have to run the fsck first to make sure that the
replicated volume is in consistent state.


Jerrybear