On Thu, 25 Mar 2010 09:01:08 +0100 Luca Berra <bluca@xxxxxxxxxx> wrote: > On Thu, Mar 25, 2010 at 11:35:43AM +1100, Neil Brown wrote: > > > > http://blogs.techrepublic.com.com/opensource/?p=1368 > > > > The most significant thing I got from this was a complain in the comments > > that managing md raid was too complex and hence error-prone. > > well, i would not be upset by j. random jerk complaining in a blog > comments, as soon as you make it one click you will find another one > that complains because it is not is favorite colour :P We can learn something from any opinion that different from our own. It is clear to me that using mdadm requires a certain level of understanding to be used effectively and safely. I don't think that can be entirely address in mdadm: there is a place of a higher level framework that encodes policies and gives advice. But there is still room to improve mdadm to make it more powerful, more informative, and more forgiving. > > > I see the issue as breaking down in to two parts. > > 1/ When a device is hot plugged into the system, is md allowed to use it as > > a spare for recovery? > > 2/ If md has a spare device, what set of arrays can it be used in if needed. > > > > A typical hot plug event will need to address both of these questions in > > turn before recovery actually starts. > > > > Part 1. > > > > A newly hotplugged device may have metadata for RAID (0.90, 1.x, IMSM, DDF, > > other vendor metadata) or LVM or a filesystem. It might have a partition > > table which could be subordinate to or super-ordinate to other metadata. > > (i.e. RAID in partitions, or partitions in RAID). The metadata may or may > > not be stale. It may or may not match - either strongly or weakly - > > metadata on devices in currently active arrays. > also the newly hotplugged device may have _data_ on it. > You mean completely raw data, no partitions, no filesystem structure etc? Yes, that is possible. People who are likely to handle devices like that would choose more conservative configurations. > > Some how from all of that information we need to decide if md can use the > > device without asking, or possibly with a simple yes/no question, and we > > need to decide what to actually do with the device. > how does the yes/no question part work? I imagine an Email to the admin "Hey boss, I just noticed you plugged in a drive that looks like it used to be part of some array. We need a spare on this other array and the new device is big enough. Shall I huh huh huh? Go on let me..." Then the admin can choose to run the command "make it so", or not. > we can also make /usr/bin/md-create-spare ... Yes, there is a place for something like that certainly. NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
