diff options
| -rw-r--r-- | debian/mdadm.docs | 1 | ||||
| -rwxr-xr-x | debian/rules | 2 | ||||
| -rw-r--r-- | md.txt | 466 |
3 files changed, 1 insertions, 468 deletions
diff --git a/debian/mdadm.docs b/debian/mdadm.docs index 2c630cb9..c06c086f 100644 --- a/debian/mdadm.docs +++ b/debian/mdadm.docs @@ -5,5 +5,4 @@ debian/README.initramfs-transition debian/README.upgrading-2.5.3 debian/README.checkarray debian/FAQ -md.txt davidpashley.com_blog_2008_07_12_rebuilding-raid.html diff --git a/debian/rules b/debian/rules index 6b8e912e..9bfa6453 100755 --- a/debian/rules +++ b/debian/rules @@ -6,7 +6,7 @@ #export DH_VERBOSE=1 -TG_BRANCHES="fixes/udev-blkid contrib/docs/raid5-vs-raid10 contrib/docs/superblock_formats" +TG_BRANCHES="fixes/udev-blkid contrib/docs/raid5-vs-raid10 contrib/docs/superblock_formats contrib/docs/md.txt" include /usr/share/quilt/quilt.make -include /usr/share/topgit/tg2quilt.mk diff --git a/md.txt b/md.txt deleted file mode 100644 index 9eb52fc8..00000000 --- a/md.txt +++ /dev/null @@ -1,466 +0,0 @@ -# linux-2.6/Documentation/md.txt -# -# From http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob_plain;f=Documentation/md.txt;hb=v2.6.26 -# -# This is md.txt for Linux kernel 2.6.26, which is current in Debian lenny. -# The latest version of this document is at -# http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob_plain;f=Documentation/md.txt;hb=HEAD - -Tools that manage md devices can be found at - http://www.<country>.kernel.org/pub/linux/utils/raid/.... - - -Boot time assembly of RAID arrays ---------------------------------- - -You can boot with your md device with the following kernel command -lines: - -for old raid arrays without persistent superblocks: - md=<md device no.>,<raid level>,<chunk size factor>,<fault level>,dev0,dev1,...,devn - -for raid arrays with persistent superblocks - md=<md device no.>,dev0,dev1,...,devn -or, to assemble a partitionable array: - md=d<md device no.>,dev0,dev1,...,devn - -md device no. = the number of the md device ... - 0 means md0, - 1 md1, - 2 md2, - 3 md3, - 4 md4 - -raid level = -1 linear mode - 0 striped mode - other modes are only supported with persistent super blocks - -chunk size factor = (raid-0 and raid-1 only) - Set the chunk size as 4k << n. - -fault level = totally ignored - -dev0-devn: e.g. /dev/hda1,/dev/hdc1,/dev/sda1,/dev/sdb1 - -A possible loadlin line (Harald Hoyer <HarryH@Royal.Net>) looks like this: - -e:\loadlin\loadlin e:\zimage root=/dev/md0 md=0,0,4,0,/dev/hdb2,/dev/hdc3 ro - - -Boot time autodetection of RAID arrays --------------------------------------- - -When md is compiled into the kernel (not as module), partitions of -type 0xfd are scanned and automatically assembled into RAID arrays. -This autodetection may be suppressed with the kernel parameter -"raid=noautodetect". As of kernel 2.6.9, only drives with a type 0 -superblock can be autodetected and run at boot time. - -The kernel parameter "raid=partitionable" (or "raid=part") means -that all auto-detected arrays are assembled as partitionable. - -Boot time assembly of degraded/dirty arrays -------------------------------------------- - -If a raid5 or raid6 array is both dirty and degraded, it could have -undetectable data corruption. This is because the fact that it is -'dirty' means that the parity cannot be trusted, and the fact that it -is degraded means that some datablocks are missing and cannot reliably -be reconstructed (due to no parity). - -For this reason, md will normally refuse to start such an array. This -requires the sysadmin to take action to explicitly start the array -despite possible corruption. This is normally done with - mdadm --assemble --force .... - -This option is not really available if the array has the root -filesystem on it. In order to support this booting from such an -array, md supports a module parameter "start_dirty_degraded" which, -when set to 1, bypassed the checks and will allows dirty degraded -arrays to be started. - -So, to boot with a root filesystem of a dirty degraded raid[56], use - - md-mod.start_dirty_degraded=1 - - -Superblock formats ------------------- - -The md driver can support a variety of different superblock formats. -Currently, it supports superblock formats "0.90.0" and the "md-1" format -introduced in the 2.5 development series. - -The kernel will autodetect which format superblock is being used. - -Superblock format '0' is treated differently to others for legacy -reasons - it is the original superblock format. - - -General Rules - apply for all superblock formats ------------------------------------------------- - -An array is 'created' by writing appropriate superblocks to all -devices. - -It is 'assembled' by associating each of these devices with an -particular md virtual device. Once it is completely assembled, it can -be accessed. - -An array should be created by a user-space tool. This will write -superblocks to all devices. It will usually mark the array as -'unclean', or with some devices missing so that the kernel md driver -can create appropriate redundancy (copying in raid1, parity -calculation in raid4/5). - -When an array is assembled, it is first initialized with the -SET_ARRAY_INFO ioctl. This contains, in particular, a major and minor -version number. The major version number selects which superblock -format is to be used. The minor number might be used to tune handling -of the format, such as suggesting where on each device to look for the -superblock. - -Then each device is added using the ADD_NEW_DISK ioctl. This -provides, in particular, a major and minor number identifying the -device to add. - -The array is started with the RUN_ARRAY ioctl. - -Once started, new devices can be added. They should have an -appropriate superblock written to them, and then passed be in with -ADD_NEW_DISK. - -Devices that have failed or are not yet active can be detached from an -array using HOT_REMOVE_DISK. - - -Specific Rules that apply to format-0 super block arrays, and - arrays with no superblock (non-persistent). -------------------------------------------------------------- - -An array can be 'created' by describing the array (level, chunksize -etc) in a SET_ARRAY_INFO ioctl. This must has major_version==0 and -raid_disks != 0. - -Then uninitialized devices can be added with ADD_NEW_DISK. The -structure passed to ADD_NEW_DISK must specify the state of the device -and it's role in the array. - -Once started with RUN_ARRAY, uninitialized spares can be added with -HOT_ADD_DISK. - - - -MD devices in sysfs -------------------- -md devices appear in sysfs (/sys) as regular block devices, -e.g. - /sys/block/md0 - -Each 'md' device will contain a subdirectory called 'md' which -contains further md-specific information about the device. - -All md devices contain: - level - a text file indicating the 'raid level'. e.g. raid0, raid1, - raid5, linear, multipath, faulty. - If no raid level has been set yet (array is still being - assembled), the value will reflect whatever has been written - to it, which may be a name like the above, or may be a number - such as '0', '5', etc. - - raid_disks - a text file with a simple number indicating the number of devices - in a fully functional array. If this is not yet known, the file - will be empty. If an array is being resized (not currently - possible) this will contain the larger of the old and new sizes. - Some raid level (RAID1) allow this value to be set while the - array is active. This will reconfigure the array. Otherwise - it can only be set while assembling an array. - - chunk_size - This is the size if bytes for 'chunks' and is only relevant to - raid levels that involve striping (1,4,5,6,10). The address space - of the array is conceptually divided into chunks and consecutive - chunks are striped onto neighbouring devices. - The size should be at least PAGE_SIZE (4k) and should be a power - of 2. This can only be set while assembling an array - - layout - The "layout" for the array for the particular level. This is - simply a number that is interpretted differently by different - levels. It can be written while assembling an array. - - reshape_position - This is either "none" or a sector number within the devices of - the array where "reshape" is up to. If this is set, the three - attributes mentioned above (raid_disks, chunk_size, layout) can - potentially have 2 values, an old and a new value. If these - values differ, reading the attribute returns - new (old) - and writing will effect the 'new' value, leaving the 'old' - unchanged. - - component_size - For arrays with data redundancy (i.e. not raid0, linear, faulty, - multipath), all components must be the same size - or at least - there must a size that they all provide space for. This is a key - part or the geometry of the array. It is measured in sectors - and can be read from here. Writing to this value may resize - the array if the personality supports it (raid1, raid5, raid6), - and if the component drives are large enough. - - metadata_version - This indicates the format that is being used to record metadata - about the array. It can be 0.90 (traditional format), 1.0, 1.1, - 1.2 (newer format in varying locations) or "none" indicating that - the kernel isn't managing metadata at all. - - resync_start - The point at which resync should start. If no resync is needed, - this will be a very large number. At array creation it will - default to 0, though starting the array as 'clean' will - set it much larger. - - new_dev - This file can be written but not read. The value written should - be a block device number as major:minor. e.g. 8:0 - This will cause that device to be attached to the array, if it is - available. It will then appear at md/dev-XXX (depending on the - name of the device) and further configuration is then possible. - - safe_mode_delay - When an md array has seen no write requests for a certain period - of time, it will be marked as 'clean'. When another write - request arrives, the array is marked as 'dirty' before the write - commences. This is known as 'safe_mode'. - The 'certain period' is controlled by this file which stores the - period as a number of seconds. The default is 200msec (0.200). - Writing a value of 0 disables safemode. - - array_state - This file contains a single word which describes the current - state of the array. In many cases, the state can be set by - writing the word for the desired state, however some states - cannot be explicitly set, and some transitions are not allowed. - - clear - No devices, no size, no level - Writing is equivalent to STOP_ARRAY ioctl - inactive - May have some settings, but array is not active - all IO results in error - When written, doesn't tear down array, but just stops it - suspended (not supported yet) - All IO requests will block. The array can be reconfigured. - Writing this, if accepted, will block until array is quiessent - readonly - no resync can happen. no superblocks get written. - write requests fail - read-auto - like readonly, but behaves like 'clean' on a write request. - - clean - no pending writes, but otherwise active. - When written to inactive array, starts without resync - If a write request arrives then - if metadata is known, mark 'dirty' and switch to 'active'. - if not known, block and switch to write-pending - If written to an active array that has pending writes, then fails. - active - fully active: IO and resync can be happening. - When written to inactive array, starts with resync - - write-pending - clean, but writes are blocked waiting for 'active' to be written. - - active-idle - like active, but no writes have been seen for a while (safe_mode_delay). - - -As component devices are added to an md array, they appear in the 'md' -directory as new directories named - dev-XXX -where XXX is a name that the kernel knows for the device, e.g. hdb1. -Each directory contains: - - block - a symlink to the block device in /sys/block, e.g. - /sys/block/md0/md/dev-hdb1/block -> ../../../../block/hdb/hdb1 - - super - A file containing an image of the superblock read from, or - written to, that device. - - state - A file recording the current state of the device in the array - which can be a comma separated list of - faulty - device has been kicked from active use due to - a detected fault - in_sync - device is a fully in-sync member of the array - writemostly - device will only be subject to read - requests if there are no other options. - This applies only to raid1 arrays. - spare - device is working, but not a full member. - This includes spares that are in the process - of being recovered to - This list may grow in future. - This can be written to. - Writing "faulty" simulates a failure on the device. - Writing "remove" removes the device from the array. - Writing "writemostly" sets the writemostly flag. - Writing "-writemostly" clears the writemostly flag. - - errors - An approximate count of read errors that have been detected on - this device but have not caused the device to be evicted from - the array (either because they were corrected or because they - happened while the array was read-only). When using version-1 - metadata, this value persists across restarts of the array. - - This value can be written while assembling an array thus - providing an ongoing count for arrays with metadata managed by - userspace. - - slot - This gives the role that the device has in the array. It will - either be 'none' if the device is not active in the array - (i.e. is a spare or has failed) or an integer less than the - 'raid_disks' number for the array indicating which position - it currently fills. This can only be set while assembling an - array. A device for which this is set is assumed to be working. - - offset - This gives the location in the device (in sectors from the - start) where data from the array will be stored. Any part of - the device before this offset us not touched, unless it is - used for storing metadata (Formats 1.1 and 1.2). - - size - The amount of the device, after the offset, that can be used - for storage of data. This will normally be the same as the - component_size. This can be written while assembling an - array. If a value less than the current component_size is - written, component_size will be reduced to this value. - - -An active md device will also contain and entry for each active device -in the array. These are named - - rdNN - -where 'NN' is the position in the array, starting from 0. -So for a 3 drive array there will be rd0, rd1, rd2. -These are symbolic links to the appropriate 'dev-XXX' entry. -Thus, for example, - cat /sys/block/md*/md/rd*/state -will show 'in_sync' on every line. - - - -Active md devices for levels that support data redundancy (1,4,5,6) -also have - - sync_action - a text file that can be used to monitor and control the rebuild - process. It contains one word which can be one of: - resync - redundancy is being recalculated after unclean - shutdown or creation - recover - a hot spare is being built to replace a - failed/missing device - idle - nothing is happening - check - A full check of redundancy was requested and is - happening. This reads all block and checks - them. A repair may also happen for some raid - levels. - repair - A full check and repair is happening. This is - similar to 'resync', but was requested by the - user, and the write-intent bitmap is NOT used to - optimise the process. - - This file is writable, and each of the strings that could be - read are meaningful for writing. - - 'idle' will stop an active resync/recovery etc. There is no - guarantee that another resync/recovery may not be automatically - started again, though some event will be needed to trigger - this. - 'resync' or 'recovery' can be used to restart the - corresponding operation if it was stopped with 'idle'. - 'check' and 'repair' will start the appropriate process - providing the current state is 'idle'. - - mismatch_count - When performing 'check' and 'repair', and possibly when - performing 'resync', md will count the number of errors that are - found. The count in 'mismatch_cnt' is the number of sectors - that were re-written, or (for 'check') would have been - re-written. As most raid levels work in units of pages rather - than sectors, this my be larger than the number of actual errors - by a factor of the number of sectors in a page. - - bitmap_set_bits - If the array has a write-intent bitmap, then writing to this - attribute can set bits in the bitmap, indicating that a resync - would need to check the corresponding blocks. Either individual - numbers or start-end pairs can be written. Multiple numbers - can be separated by a space. - Note that the numbers are 'bit' numbers, not 'block' numbers. - They should be scaled by the bitmap_chunksize. - - sync_speed_min - sync_speed_max - This are similar to /proc/sys/dev/raid/speed_limit_{min,max} - however they only apply to the particular array. - If no value has been written to these, of if the word 'system' - is written, then the system-wide value is used. If a value, - in kibibytes-per-second is written, then it is used. - When the files are read, they show the currently active value - followed by "(local)" or "(system)" depending on whether it is - a locally set or system-wide value. - - sync_completed - This shows the number of sectors that have been completed of - whatever the current sync_action is, followed by the number of - sectors in total that could need to be processed. The two - numbers are separated by a '/' thus effectively showing one - value, a fraction of the process that is complete. - A 'select' on this attribute will return when resync completes, - when it reaches the current sync_max (below) and possibly at - other times. - - sync_max - This is a number of sectors at which point a resync/recovery - process will pause. When a resync is active, the value can - only ever be increased, never decreased. The value of 'max' - effectively disables the limit. - - - sync_speed - This shows the current actual speed, in K/sec, of the current - sync_action. It is averaged over the last 30 seconds. - - suspend_lo - suspend_hi - The two values, given as numbers of sectors, indicate a range - within the array where IO will be blocked. This is currently - only supported for raid4/5/6. - - -Each active md device may also have attributes specific to the -personality module that manages it. -These are specific to the implementation of the module and could -change substantially if the implementation changes. - -These currently include - - stripe_cache_size (currently raid5 only) - number of entries in the stripe cache. This is writable, but - there are upper and lower limits (32768, 16). Default is 128. - strip_cache_active (currently raid5 only) - number of active entries in the stripe cache - preread_bypass_threshold (currently raid5 only) - number of times a stripe requiring preread will be bypassed by - a stripe that does not require preread. For fairness defaults - to 1. Setting this to 0 disables bypass accounting and - requires preread stripes to wait until all full-width stripe- - writes are complete. Valid values are 0 to stripe_cache_size. |