Hello all,
I have a customer who is adamant that there is some software or
hardware or combination of both that allows the secondary volume of a
mirror to instantaneously see the data that was created on the primary.
In all of my experience with both Windows and UNIX environments I have
not come across anything that does this.
Of course, the mirror can be created at the hardware level and in that
sense it is an exact mirror. However, in order for the filesystem to be
able to pick up the synced data it must be unmounted and then
remounted, usually with an fsck on UNIX prior to remounting.
This applies to whether or not the mirrored volume is on the same host
or a different host altogether.
Can anyone dispute this, if so can you tell me how the software is able
to pick up the changes to the volume and push it up to the filesystem
level dynamically?
Also, can anyone give me a good explanation of why this isn't possible
if this turns out to be the case? I believe it has to do with the
filesystem needing to reread in its inode table but can't say for sure.

Thanks for any advice.

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