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Diffstat (limited to 'Documentation/device-mapper/dm-log.txt')
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diff --git a/Documentation/device-mapper/dm-log.txt b/Documentation/device-mapper/dm-log.txt deleted file mode 100644 index c155ac569c44..000000000000 --- a/Documentation/device-mapper/dm-log.txt +++ /dev/null @@ -1,54 +0,0 @@ -Device-Mapper Logging -===================== -The device-mapper logging code is used by some of the device-mapper -RAID targets to track regions of the disk that are not consistent. -A region (or portion of the address space) of the disk may be -inconsistent because a RAID stripe is currently being operated on or -a machine died while the region was being altered. In the case of -mirrors, a region would be considered dirty/inconsistent while you -are writing to it because the writes need to be replicated for all -the legs of the mirror and may not reach the legs at the same time. -Once all writes are complete, the region is considered clean again. - -There is a generic logging interface that the device-mapper RAID -implementations use to perform logging operations (see -dm_dirty_log_type in include/linux/dm-dirty-log.h). Various different -logging implementations are available and provide different -capabilities. The list includes: - -Type Files -==== ===== -disk drivers/md/dm-log.c -core drivers/md/dm-log.c -userspace drivers/md/dm-log-userspace* include/linux/dm-log-userspace.h - -The "disk" log type -------------------- -This log implementation commits the log state to disk. This way, the -logging state survives reboots/crashes. - -The "core" log type -------------------- -This log implementation keeps the log state in memory. The log state -will not survive a reboot or crash, but there may be a small boost in -performance. This method can also be used if no storage device is -available for storing log state. - -The "userspace" log type ------------------------- -This log type simply provides a way to export the log API to userspace, -so log implementations can be done there. This is done by forwarding most -logging requests to userspace, where a daemon receives and processes the -request. - -The structure used for communication between kernel and userspace are -located in include/linux/dm-log-userspace.h. Due to the frequency, -diversity, and 2-way communication nature of the exchanges between -kernel and userspace, 'connector' is used as the interface for -communication. - -There are currently two userspace log implementations that leverage this -framework - "clustered-disk" and "clustered-core". These implementations -provide a cluster-coherent log for shared-storage. Device-mapper mirroring -can be used in a shared-storage environment when the cluster log implementations -are employed. |