None of the solutions being talked about perform "failing over" in userland. The RAID transforms which perform this operation are kernel resident in DM, MD, and EMD. Perhaps you are talking about spare activation and rebuild?
This is precisely why I sent the second email, and made the qualification I did :)
For a "do it in userland" solution, an initrd or initramfs piece examines the system configuration, and assembles physical disks into RAID arrays based on the information it finds. I was mainly implying that an initrd solution would have to provide some primitive failover initially, before the kernel is bootstrapped... much like a bootloader that supports booting off a RAID1 array would need to do.
"Failover" (i.e. redirecting a read to a viable member) will not occur via userland at all. The initrd solution just has to present all available members to the kernel interface performing the RAID transform. There is no need for "special failover handling" during bootstrap in either case.
hmmm, yeah, agreed.
Jeff
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