On Fri, Jun 01, 2007 at 10:46:19AM +0200, Andi Kleen wrote: > > That will make laptop users very unhappy if you spin up their disks > every 5 seconds. And even on other systems it might reduce the MTBF > if you write the super block much more often than before. It might > be better to set it up in some way to only increase that number when > the super block is written for some other reason anyways. You would never want to use this feature on a laptop; it would buy no benefit for its costs, since with (all common) laptops, their hard drives can't be shared with other machines in a cluster. Unfortunately, it's not possible to do what you suggest, since one of the whole points of increasing the sequence number every 5 seconds is to act as a keep-alive, so another machine trying to access the shared hard drive can tell whether or not the machine which currently had the hard drive mounted is still alive or not. This is why I and others have been a little worried about implementing this feature, since it adds complexity which has to be in a proper HA system anyway, and what is there isn't really an optimal HA solution (since it lacks STONITH) and so you have to implement the functionality again _anyway_ using a proper HA solution. The argument on the other side is that it protects against failed HA solutions, and against users who are too stupid to know that they need an HA solution. It does do the first; the second would only apply if the users who were too stupid to realize they needed an HA solution, were smart enough to enable it the MMP feature --- and because of its many costs, including keeping the disk spun up on laptops, and delaying the time required to mount the disk by 10 seconds, I don't think it will ever be enabled by default. Hence, I don't really think it helps the idiotic user problem. But apparently a belt-and-suspenders approach to HA is comforting to some users, and so I don't mind reserving the space. The code to implement it still seems like more complexity than what should be in the kernel. My suggestion would be to put it in a separate file, and make it be something which has to be explicitly configured to enable it, possibly as a module (but that may add too much extra hair). I really don't think the save-the-stupid-user argument holds water, but the belt-and-suspenders argument IFF you are using a shared-disk setup is a valid, although probably not a common setup. Regards, - Ted - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
