>>>>> "Michael" == Michael Tokarev <mjt@xxxxxxxxxx> writes: Michael> Doug Ledford wrote: Michael> [] >> 1.0, 1.1, and 1.2 are the same format, just in different positions on >> the disk. Of the three, the 1.1 format is the safest to use since it >> won't allow you to accidentally have some sort of metadata between the >> beginning of the disk and the raid superblock (such as an lvm2 >> superblock), and hence whenever the raid array isn't up, you won't be >> able to accidentally mount the lvm2 volumes, filesystem, etc. (In worse >> case situations, I've seen lvm2 find a superblock on one RAID1 array >> member when the RAID1 array was down, the system came up, you used the >> system, the two copies of the raid array were made drastically >> inconsistent, then at the next reboot, the situation that prevented the >> RAID1 from starting was resolved, and it never know it failed to start >> last time, and the two inconsistent members we put back into a clean >> array). So, deprecating any of these is not really helpful. And you >> need to keep the old 0.90 format around for back compatibility with >> thousands of existing raid arrays. Michael> Well, I strongly, completely disagree. You described a Michael> real-world situation, and that's unfortunate, BUT: for at Michael> least raid1, there ARE cases, pretty valid ones, when one Michael> NEEDS to mount the filesystem without bringing up raid. Michael> Raid1 allows that. Please describe one such case please. There have certainly been hacks of various RAID systems on other OSes such as Solaris where the VxVM and/or Solstice DiskSuite allowed you to encapsulate an existing partition into a RAID array. But in my experience (and I'm a professional sysadm... :-) it's not really all that useful, and can lead to problems liks those described by Doug. If you are going to mirror an existing filesystem, then by definition you have a second disk or partition available for the purpose. So you would merely setup the new RAID1, in degraded mode, using the new partition as the base. Then you copy the data over to the new RAID1 device, change your boot setup, and reboot. Once that is done, you can then add the original partition into the RAID1 array. As Doug says, and I agree strongly, you DO NOT want to have the possibility of confusion and data loss, especially on bootup. And this leads to the heart of my initial post on this matter, that the confusion of having four different variations of RAID superblocks is bad. We should deprecate them down to just two, the old 0.90 format, and the new 1.x format at the start of the RAID volume. John - 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
