diff options
Diffstat (limited to 'Documentation/device-mapper')
| -rw-r--r-- | Documentation/device-mapper/cache.txt | 6 | ||||
| -rw-r--r-- | Documentation/device-mapper/statistics.txt | 186 | ||||
| -rw-r--r-- | Documentation/device-mapper/thin-provisioning.txt | 15 |
3 files changed, 198 insertions, 9 deletions
diff --git a/Documentation/device-mapper/cache.txt b/Documentation/device-mapper/cache.txt index e8cdf7241b66..33d45ee0b737 100644 --- a/Documentation/device-mapper/cache.txt +++ b/Documentation/device-mapper/cache.txt @@ -50,14 +50,16 @@ other parameters detailed later): which are dirty, and extra hints for use by the policy object. This information could be put on the cache device, but having it separate allows the volume manager to configure it differently, - e.g. as a mirror for extra robustness. + e.g. as a mirror for extra robustness. This metadata device may only + be used by a single cache device. Fixed block size ---------------- The origin is divided up into blocks of a fixed size. This block size is configurable when you first create the cache. Typically we've been -using block sizes of 256k - 1024k. +using block sizes of 256KB - 1024KB. The block size must be between 64 +(32KB) and 2097152 (1GB) and a multiple of 64 (32KB). Having a fixed block size simplifies the target a lot. But it is something of a compromise. For instance, a small part of a block may be diff --git a/Documentation/device-mapper/statistics.txt b/Documentation/device-mapper/statistics.txt new file mode 100644 index 000000000000..2a1673adc200 --- /dev/null +++ b/Documentation/device-mapper/statistics.txt @@ -0,0 +1,186 @@ +DM statistics +============= + +Device Mapper supports the collection of I/O statistics on user-defined +regions of a DM device. If no regions are defined no statistics are +collected so there isn't any performance impact. Only bio-based DM +devices are currently supported. + +Each user-defined region specifies a starting sector, length and step. +Individual statistics will be collected for each step-sized area within +the range specified. + +The I/O statistics counters for each step-sized area of a region are +in the same format as /sys/block/*/stat or /proc/diskstats (see: +Documentation/iostats.txt). But two extra counters (12 and 13) are +provided: total time spent reading and writing in milliseconds. All +these counters may be accessed by sending the @stats_print message to +the appropriate DM device via dmsetup. + +Each region has a corresponding unique identifier, which we call a +region_id, that is assigned when the region is created. The region_id +must be supplied when querying statistics about the region, deleting the +region, etc. Unique region_ids enable multiple userspace programs to +request and process statistics for the same DM device without stepping +on each other's data. + +The creation of DM statistics will allocate memory via kmalloc or +fallback to using vmalloc space. At most, 1/4 of the overall system +memory may be allocated by DM statistics. The admin can see how much +memory is used by reading +/sys/module/dm_mod/parameters/stats_current_allocated_bytes + +Messages +======== + + @stats_create <range> <step> [<program_id> [<aux_data>]] + + Create a new region and return the region_id. + + <range> + "-" - whole device + "<start_sector>+<length>" - a range of <length> 512-byte sectors + starting with <start_sector>. + + <step> + "<area_size>" - the range is subdivided into areas each containing + <area_size> sectors. + "/<number_of_areas>" - the range is subdivided into the specified + number of areas. + + <program_id> + An optional parameter. A name that uniquely identifies + the userspace owner of the range. This groups ranges together + so that userspace programs can identify the ranges they + created and ignore those created by others. + The kernel returns this string back in the output of + @stats_list message, but it doesn't use it for anything else. + + <aux_data> + An optional parameter. A word that provides auxiliary data + that is useful to the client program that created the range. + The kernel returns this string back in the output of + @stats_list message, but it doesn't use this value for anything. + + @stats_delete <region_id> + + Delete the region with the specified id. + + <region_id> + region_id returned from @stats_create + + @stats_clear <region_id> + + Clear all the counters except the in-flight i/o counters. + + <region_id> + region_id returned from @stats_create + + @stats_list [<program_id>] + + List all regions registered with @stats_create. + + <program_id> + An optional parameter. + If this parameter is specified, only matching regions + are returned. + If it is not specified, all regions are returned. + + Output format: + <region_id>: <start_sector>+<length> <step> <program_id> <aux_data> + + @stats_print <region_id> [<starting_line> <number_of_lines>] + + Print counters for each step-sized area of a region. + + <region_id> + region_id returned from @stats_create + + <starting_line> + The index of the starting line in the output. + If omitted, all lines are returned. + + <number_of_lines> + The number of lines to include in the output. + If omitted, all lines are returned. + + Output format for each step-sized area of a region: + + <start_sector>+<length> counters + + The first 11 counters have the same meaning as + /sys/block/*/stat or /proc/diskstats. + + Please refer to Documentation/iostats.txt for details. + + 1. the number of reads completed + 2. the number of reads merged + 3. the number of sectors read + 4. the number of milliseconds spent reading + 5. the number of writes completed + 6. the number of writes merged + 7. the number of sectors written + 8. the number of milliseconds spent writing + 9. the number of I/Os currently in progress + 10. the number of milliseconds spent doing I/Os + 11. the weighted number of milliseconds spent doing I/Os + + Additional counters: + 12. the total time spent reading in milliseconds + 13. the total time spent writing in milliseconds + + @stats_print_clear <region_id> [<starting_line> <number_of_lines>] + + Atomically print and then clear all the counters except the + in-flight i/o counters. Useful when the client consuming the + statistics does not want to lose any statistics (those updated + between printing and clearing). + + <region_id> + region_id returned from @stats_create + + <starting_line> + The index of the starting line in the output. + If omitted, all lines are printed and then cleared. + + <number_of_lines> + The number of lines to process. + If omitted, all lines are printed and then cleared. + + @stats_set_aux <region_id> <aux_data> + + Store auxiliary data aux_data for the specified region. + + <region_id> + region_id returned from @stats_create + + <aux_data> + The string that identifies data which is useful to the client + program that created the range. The kernel returns this + string back in the output of @stats_list message, but it + doesn't use this value for anything. + +Examples +======== + +Subdivide the DM device 'vol' into 100 pieces and start collecting +statistics on them: + + dmsetup message vol 0 @stats_create - /100 + +Set the auxillary data string to "foo bar baz" (the escape for each +space must also be escaped, otherwise the shell will consume them): + + dmsetup message vol 0 @stats_set_aux 0 foo\\ bar\\ baz + +List the statistics: + + dmsetup message vol 0 @stats_list + +Print the statistics: + + dmsetup message vol 0 @stats_print 0 + +Delete the statistics: + + dmsetup message vol 0 @stats_delete 0 diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt index 30b8b83bd333..50c44cf79b0e 100644 --- a/Documentation/device-mapper/thin-provisioning.txt +++ b/Documentation/device-mapper/thin-provisioning.txt @@ -99,13 +99,14 @@ Using an existing pool device $data_block_size $low_water_mark" $data_block_size gives the smallest unit of disk space that can be -allocated at a time expressed in units of 512-byte sectors. People -primarily interested in thin provisioning may want to use a value such -as 1024 (512KB). People doing lots of snapshotting may want a smaller value -such as 128 (64KB). If you are not zeroing newly-allocated data, -a larger $data_block_size in the region of 256000 (128MB) is suggested. -$data_block_size must be the same for the lifetime of the -metadata device. +allocated at a time expressed in units of 512-byte sectors. +$data_block_size must be between 128 (64KB) and 2097152 (1GB) and a +multiple of 128 (64KB). $data_block_size cannot be changed after the +thin-pool is created. People primarily interested in thin provisioning +may want to use a value such as 1024 (512KB). People doing lots of +snapshotting may want a smaller value such as 128 (64KB). If you are +not zeroing newly-allocated data, a larger $data_block_size in the +region of 256000 (128MB) is suggested. $low_water_mark is expressed in blocks of size $data_block_size. If free space on the data device drops below this level then a dm event |