This series of patches implements the Partial Parity Log for RAID5 arrays. The purpose of this feature is closing the RAID Write Hole. It is a solution alternative to the existing raid5-cache, but the implementation is based on it and reuses some of the code by introducing support for interchangeable policies. This allows decoupling policy from mechanism and not adding more boilerplate code in raid5.c. The issue addressed by PPL is, that on a dirty shutdown, parity for a particular stripe may be inconsistent with data on other member disks. In degraded state, there is no way to recalculate parity, because one of the disks is missing. PPL addresses this issue and allows recalculating the parity. It stores only enough data needed for recovering from RWH and is not a true journal, like the raid5-cache implementation. It does not protect from losing in-flight data. PPL is a distributed log - data is stored on all RAID member drives in the metadata area. It does not need a dedicated journaling drive. Performance is reduced by up to 30%-40% but it scales with the number of drives in the array and the journaling drive does not become a bottleneck. This feature originated from Intel RSTe, which uses IMSM metadata. This patchset implements PPL for external metadata (specifically IMSM) as well as native MD v1.1 and v1.2 metadata. Thanks, Artur Artur Paszkiewicz (12): raid5-cache: move declarations to separate header raid5-cache: add policy logic raid5-cache: add a new policy md: superblock changes for PPL raid5-ppl: Partial Parity Log implementation raid5-ppl: calculate partial parity md: mddev_find_container helper function md: expose rdev->sb_start as sysfs attribute raid5-ppl: read PPL signature from IMSM metadata raid5-ppl: recovery from dirty shutdown using PPL raid5-ppl: support disk add/remove with distributed PPL raid5-ppl: runtime PPL enabling or disabling drivers/md/Makefile | 2 +- drivers/md/md.c | 81 ++- drivers/md/md.h | 14 + drivers/md/raid5-cache.c | 276 +++++----- drivers/md/raid5-cache.h | 171 ++++++ drivers/md/raid5-ppl.c | 1123 ++++++++++++++++++++++++++++++++++++++++ drivers/md/raid5.c | 274 +++++++++- drivers/md/raid5.h | 10 +- include/uapi/linux/raid/md_p.h | 18 +- 9 files changed, 1786 insertions(+), 183 deletions(-) create mode 100644 drivers/md/raid5-cache.h create mode 100644 drivers/md/raid5-ppl.c -- 2.10.1 -- 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
