Benoît Canet <benoit.ca...@gmail.com> writes: > This patchset create a block driver implementing a qorum using three qemu disk > images. Writes are mirrored on the three files. > For the reading part the three files are read at the same time and a vote is > done to determine which is the majoritary qiov version. It then return this > majoritary version to the upper layers. > When three differents versions of the data are returned by the lower layer the > qorum is broken and the read return -EIO. > > The goal of this patchset is to be turned in a QEMU block filter living just > above raw-*.c and below qcow2/qed when the required infrastructure will be > done. > > Main use of this feature will be people using NFS appliances which can be > subjected to bitflip errors.
I'm not entirely sure I understand the use-case all that well. Wouldn't the more typical approach be RAID-5 and the use of parity instead of relying on voting? Quorum doesn't work well with an odd number of disks whereas RAID-5 does. You also get significantly more usable disk space with RAID-5 then with voting. Regards, Anthony Liguori
