MD(4)                                                                                                                                                              MD(4)

NAME

       md - Multiple Device driver aka Linux Software RAID

SYNOPSIS

       /dev/mdn
       /dev/md/n
       /dev/md/name

DESCRIPTION

       The md driver provides virtual devices that are created from one or more independent underlying devices.  This array of devices often contains redundancy and the
       devices are often disk drives, hence the acronym RAID which stands for a Redundant Array of Independent Disks.

       md supports RAID levels 1 (mirroring), 4 (striped array with parity device), 5 (striped array  with  distributed  parity  information),  6  (striped  array  with
       distributed  dual  redundancy information), and 10 (striped and mirrored).  If some number of underlying devices fails while using one of these levels, the array
       will continue to function; this number is one for RAID levels 4 and 5, two for RAID level 6,  and  all  but  one  (N-1)  for  RAID  level  1,  and  dependent  on
       configuration for level 10.

       md  also supports a number of pseudo RAID (non-redundant) configurations including RAID0 (striped array), LINEAR (catenated array), MULTIPATH (a set of different
       interfaces to the same device), and FAULTY (a layer over a single device into which errors can be injected).

   MD METADATA
       Each device in an array may have some metadata stored in the device.  This metadata is sometimes called a superblock.  The metadata records information about the
       structure and state of the array.  This allows the array to be reliably re-assembled after a shutdown.

       From  Linux  kernel  version  2.6.10, md provides support for two different formats of metadata, and other formats can be added.  Prior to this release, only one
       format is supported.

       The common format -- known as version 0.90 -- has a superblock that is 4K long and is written into a 64K aligned block that starts at least  64K  and  less  than
       128K  from  the  end of the device (i.e. to get the address of the superblock round the size of the device down to a multiple of 64K and then subtract 64K).  The
       available size of each device is the amount of space before the super block, so between 64K and 128K is lost when a device in  incorporated  into  an  MD  array.
       This superblock stores multi-byte fields in a processor-dependent manner, so arrays cannot easily be moved between computers with different processors.

       The  new  format -- known as version 1 -- has a superblock that is normally 1K long, but can be longer.  It is normally stored between 8K and 12K from the end of
       the device, on a 4K boundary, though variations can be stored at the start of the device (version 1.1) or 4K from the start of the device  (version  1.2).   This
       metadata format stores multibyte data in a processor-independent format and supports up to hundreds of component devices (version 0.90 only supports 28).

       The metadata contains, among other things:

       LEVEL  The manner in which the devices are arranged into the array (linear, raid0, raid1, raid4, raid5, raid10, multipath).

       UUID   a 128 bit Universally Unique Identifier that identifies the array that contains this device.

       When  a  version  0.90  array  is being reshaped (e.g. adding extra devices to a RAID5), the version number is temporarily set to 0.91.  This ensures that if the
       reshape process is stopped in the middle (e.g. by a system crash) and the machine boots into an older kernel that does not support reshaping, then the array will
       not be assembled (which would cause data corruption) but will be left untouched until a kernel that can complete the reshape processes is used.

   ARRAYS WITHOUT METADATA
       While it is usually best to create arrays with superblocks so that they can be assembled reliably, there are some circumstances when an array without superblocks
       is preferred.  These include:

       LEGACY ARRAYS
              Early versions of the md driver only supported Linear and Raid0 configurations  and  did  not  use  a  superblock  (which  is  less  critical  with  these
              configurations).  While such arrays should be rebuilt with superblocks if possible, md continues to support them.

       FAULTY Being a largely transparent layer over a different device, the FAULTY personality doesn't gain anything from having a superblock.

       MULTIPATH
              It  is  often possible to detect devices which are different paths to the same storage directly rather than having a distinctive superblock written to the
              device and searched for on all paths.  In this case, a MULTIPATH array with no superblock makes sense.

       RAID1  In some configurations it might be desired to create a raid1 configuration that does not use a  superblock,  and  to  maintain  the  state  of  the  array
              elsewhere.  While not encouraged for general use, it does have special-purpose uses and is supported.

   ARRAYS WITH EXTERNAL METADATA
       From  release  2.6.28,  the md driver supports arrays with externally managed metadata.  That is, the metadata is not managed by the kernel but rather by a user-
       space program which is external to the kernel.  This allows support for a variety of metadata formats without cluttering the kernel with lots of details.

       md is able to communicate with the user-space program through various sysfs attributes so that it can make appropriate changes to the metadata - for  example  to
       mark  a  device  as faulty.  When necessary, md will wait for the program to acknowledge the event by writing to a sysfs attribute.  The manual page for mdmon(8)
       contains more detail about this interaction.

   CONTAINERS
       Many metadata formats use a single block of metadata to describe a number of different arrays which all use the same set of devices.  In this case it is  helpful
       for  the  kernel  to  know about the full set of devices as a whole.  This set is known to md as a container.  A container is an md array with externally managed
       metadata and with device offset and size so that it just covers the metadata part of the devices.  The remainder of each device is available to  be  incorporated
       into various arrays.

   LINEAR
       A linear array simply catenates the available space on each drive to form one large virtual drive.

       One  advantage of this arrangement over the more common RAID0 arrangement is that the array may be reconfigured at a later time with an extra drive, so the array
       is made bigger without disturbing the data that is on the array.  This can even be done on a live array.

       If a chunksize is given with a LINEAR array, the usable space on each device is rounded down to a multiple of this chunksize.

   RAID0
       A RAID0 array (which has zero redundancy) is also known as a striped array.  A RAID0 array is configured at creation with a Chunk Size which must be a  power  of
       two (prior to Linux 2.6.31), and at least 4 kibibytes.

       The  RAID0  driver assigns the first chunk of the array to the first device, the second chunk to the second device, and so on until all drives have been assigned
       one chunk.  This collection of chunks forms a stripe.  Further chunks are gathered into stripes in the same way, and are assigned to the remaining space  in  the
       drives.

       If  devices  in  the  array  are  not all the same size, then once the smallest device has been exhausted, the RAID0 driver starts collecting chunks into smaller
       stripes that only span the drives which still have remaining space.

   RAID1
       A RAID1 array is also known as a mirrored set (though mirrors tend to provide reflected images, which RAID1 does not) or a plex.

       Once initialised, each device in a RAID1 array contains exactly the same data.  Changes are written to all devices in  parallel.   Data  is  read  from  any  one
       device.  The driver attempts to distribute read requests across all devices to maximise performance.

       All  devices  in a RAID1 array should be the same size.  If they are not, then only the amount of space available on the smallest device is used (any extra space
       on other devices is wasted).

       Note that the read balancing done by the driver does not make the RAID1 performance profile be the same as for RAID0; a single stream of  sequential  input  will
       not  be  accelerated  (e.g.  a single dd), but multiple sequential streams or a random workload will use more than one spindle. In theory, having an N-disk RAID1
       will allow N sequential threads to read from all disks.

       Individual devices in a RAID1 can be marked as "write-mostly".  These drives are excluded from the normal read balancing and will only be read from when there is
       no other option.  This can be useful for devices connected over a slow link.

   RAID4
       A RAID4 array is like a RAID0 array with an extra device for storing parity. This device is the last of the active devices in the array. Unlike RAID0, RAID4 also
       requires that all stripes span all drives, so extra space on devices that are larger than the smallest is wasted.

       When any block in a RAID4 array is modified, the parity block for that stripe (i.e. the block in the parity device at the same device offset as  the  stripe)  is
       also  modified  so  that  the  parity  block  always  contains  the "parity" for the whole stripe.  I.e. its content is equivalent to the result of performing an
       exclusive-or operation between all the data blocks in the stripe.

       This allows the array to continue to function if one device fails.  The data that was on that device can be calculated as needed from the parity  block  and  the
       other data blocks.

   RAID5
       RAID5  is  very  similar  to  RAID4.   The  difference is that the parity blocks for each stripe, instead of being on a single device, are distributed across all
       devices.  This allows more parallelism when writing, as two different block updates will quite possibly affect parity blocks on different  devices  so  there  is
       less contention.

       This also allows more parallelism when reading, as read requests are distributed over all the devices in the array instead of all but one.

   RAID6
       RAID6 is similar to RAID5, but can handle the loss of any two devices without data loss.  Accordingly, it requires N+2 drives to store N drives worth of data.

       The  performance  for  RAID6  is  slightly lower but comparable to RAID5 in normal mode and single disk failure mode.  It is very slow in dual disk failure mode,
       however.

   RAID10
       RAID10 provides a combination of RAID1 and RAID0, and is sometimes known as RAID1+0.  Every datablock is duplicated some  number  of  times,  and  the  resulting
       collection of datablocks are distributed over multiple drives.

       When configuring a RAID10 array, it is necessary to specify the number of replicas of each data block that are required (this will normally be 2) and whether the
       replicas should be 'near', 'offset' or 'far'.  (Note that the 'offset' layout is only available from 2.6.18).

       When 'near' replicas are chosen, the multiple copies of a given chunk are laid out consecutively across the stripes  of  the  array,  so  the  two  copies  of  a
       datablock will likely be at the same offset on two adjacent devices.

       When  'far'  replicas  are  chosen,  the  multiple copies of a given chunk are laid out quite distant from each other.  The first copy of all data blocks will be
       striped across the early part of all drives in RAID0 fashion, and then the next copy of all blocks will be striped across a later section of all  drives,  always
       ensuring that all copies of any given block are on different drives.

       The 'far' arrangement can give sequential read performance equal to that of a RAID0 array, but at the cost of reduced write performance.

       When  'offset'  replicas are chosen, the multiple copies of a given chunk are laid out on consecutive drives and at consecutive offsets.  Effectively each stripe
       is duplicated and the copies are offset by one device.   This should give similar read characteristics to 'far' if a suitably  large  chunk  size  is  used,  but
       without as much seeking for writes.

       It  should  be  noted  that the number of devices in a RAID10 array need not be a multiple of the number of replica of each data block; however, there must be at
       least as many devices as replicas.

       If, for example, an array is created with 5 devices and 2 replicas, then space equivalent to 2.5 of the devices will be available, and every block will be stored
       on two different devices.

       Finally,  it is possible to have an array with both 'near' and 'far' copies.  If an array is configured with 2 near copies and 2 far copies, then there will be a
       total of 4 copies of each block, each on a different drive.  This is an artifact of the implementation and is unlikely to be of real value.

   MULTIPATH
       MULTIPATH is not really a RAID at all as there is only one real device in a MULTIPATH md array.  However there are multiple access points (paths) to this device,
       and one of these paths might fail, so there are some similarities.

       A  MULTIPATH  array  is  composed  of a number of logically different devices, often fibre channel interfaces, that all refer the the same real device. If one of
       these interfaces fails (e.g. due to cable problems), the multipath driver will attempt to redirect requests to another interface.

       The MULTIPATH drive is not receiving any ongoing development and should be considered a legacy driver.  The  device-mapper  based  multipath  drivers  should  be
       preferred for new installations.

   FAULTY
       The FAULTY md module is provided for testing purposes.  A faulty array has exactly one component device and is normally assembled without a superblock, so the md
       array created provides direct access to all of the data in the component device.

       The FAULTY module may be requested to simulate faults to allow testing of other md levels or of filesystems.  Faults can be chosen to trigger on read requests or
       write requests, and can be transient (a subsequent read/write at the address will probably succeed) or persistent (subsequent read/write of the same address will
       fail).  Further, read faults can be "fixable" meaning that they persist until a write request at the same address.

       Fault types can be requested with a period.  In this case, the fault will recur repeatedly after the given number of requests of the relevant type.  For  example
       if  persistent read faults have a period of 100, then every 100th read request would generate a fault, and the faulty sector would be recorded so that subsequent
       reads on that sector would also fail.

       There is a limit to the number of faulty sectors that are remembered.  Faults generated after this limit is exhausted are treated as transient.

       The list of faulty sectors can be flushed, and the active list of failure modes can be cleared.

   UNCLEAN SHUTDOWN
       When changes are made to a RAID1, RAID4, RAID5, RAID6, or RAID10 array there is a possibility of inconsistency for short periods of time as each update  requires
       at  least  two  block  to  be  written to different devices, and these writes probably won't happen at exactly the same time.  Thus if a system with one of these
       arrays is shutdown in the middle of a write operation (e.g. due to power failure), the array may not be consistent.

       To handle this situation, the md driver marks an array as "dirty" before writing any data to it, and marks it as "clean" when the array is being  disabled,  e.g.
       at  shutdown.   If  the md driver finds an array to be dirty at startup, it proceeds to correct any possibly inconsistency.  For RAID1, this involves copying the
       contents of the first drive onto all other drives.  For RAID4, RAID5 and RAID6 this involves recalculating the parity for each stripe and making  sure  that  the
       parity  block  has  the  correct  data.   For  RAID10  it  involves  copying  one  of  the  replicas  of  each block onto all the others.  This process, known as
       "resynchronising" or "resync" is performed in the background.  The array can still be used, though possibly with reduced performance.

       If a RAID4, RAID5 or RAID6 array is degraded (missing at least one drive, two for RAID6) when it is restarted after an unclean shutdown,  it  cannot  recalculate
       parity,  and  so  it  is possible that data might be undetectably corrupted.  The 2.4 md driver does not alert the operator to this condition.  The 2.6 md driver
       will fail to start an array in this condition without manual intervention, though this behaviour can be overridden by a kernel parameter.

   RECOVERY
       If the md driver detects a write error on a device in a RAID1, RAID4, RAID5, RAID6, or RAID10 array, it immediately disables that device (marking it  as  faulty)
       and  continues  operation on the remaining devices.  If there are spare drives, the driver will start recreating on one of the spare drives the data which was on
       that failed drive, either by copying a working drive in a RAID1 configuration, or by doing calculations with the parity block on RAID4, RAID5  or  RAID6,  or  by
       finding and copying originals for RAID10.

       In  kernels  prior to about 2.6.15, a read error would cause the same effect as a write error.  In later kernels, a read-error will instead cause md to attempt a
       recovery by overwriting the bad block. i.e. it will find the correct data from elsewhere, write it over the block that failed, and  then  try  to  read  it  back
       again.  If either the write or the re-read fail, md will treat the error the same way that a write error is treated, and will fail the whole device.

       While  this  recovery  process  is  happening,  the  md  driver  will  monitor accesses to the array and will slow down the rate of recovery if other activity is
       happening, so that normal access to the array will not be unduly affected.  When no other activity is happening, the recovery process  proceeds  at  full  speed.
       The actual speed targets for the two different situations can be controlled by the speed_limit_min and speed_limit_max control files mentioned below.

   SCRUBBING AND MISMATCHES
       As  storage  devices  can  develop  bad  blocks at any time it is valuable to regularly read all blocks on all devices in an array so as to catch such bad blocks
       early.  This process is called scrubbing.

       md arrays can be scrubbed by writing either check or repair to the file md/sync_action in the sysfs directory for the device.

       Requesting a scrub will cause md to read every block on every device in the array, and check that the data is consistent.   For  RAID1  and  RAID10,  this  means
       checking that the copies are identical.  For RAID4, RAID5, RAID6 this means checking that the parity block is (or blocks are) correct.

       If  a read error is detected during this process, the normal read-error handling causes correct data to be found from other devices and to be written back to the
       faulty device.  In many case this will effectively fix the bad block.

       If all blocks read successfully but are found to not be consistent, then this is regarded as a mismatch.

       If check was used, then no action is taken to handle the mismatch, it is simply recorded.  If repair was used, then a mismatch will be repaired in the  same  way
       that  resync  repairs  arrays.   For RAID5/RAID6 new parity blocks are written.  For RAID1/RAID10, all but one block are overwritten with the content of that one
       block.

       A count of mismatches is recorded in the sysfs file md/mismatch_cnt.  This is set to zero when a scrub starts and is incremented whenever a sector is found  that
       is  a  mismatch.  md normally works in units much larger than a single sector and when it finds a mismatch, it does not determine exactly how many actual sectors
       were affected but simply adds the number of sectors in the IO unit that was used.  So a value of 128 could simply mean that a single 64KB check  found  an  error
       (128 x 512bytes = 64KB).

       If an array is created by mdadm with --assume-clean then a subsequent check could be expected to find some mismatches.

       On a truly clean RAID5 or RAID6 array, any mismatches should indicate a hardware problem at some level - software issues should never cause such a mismatch.

       However  on RAID1 and RAID10 it is possible for software issues to cause a mismatch to be reported.  This does not necessarily mean that the data on the array is
       corrupted.  It could simply be that the system does not care what is stored on that part of the array - it is unused space.

       The most likely cause for an unexpected mismatch on RAID1 or RAID10 occurs if a swap partition or swap file is stored on the array.

       When the swap subsystem wants to write a page of memory out, it flags the page as 'clean' in the memory manager and requests the swap device to write it out.  It
       is  quite  possible  that  the  memory  will be changed while the write-out is happening.  In that case the 'clean' flag will be found to be clear when the write
       completes and so the swap subsystem will simply forget that the swapout had been attempted, and will possibly choose a different page to write out.

       If the swap device was on RAID1 (or RAID10), then the data is sent from memory to a device twice (or more depending on the number of devices in the array).  Thus
       it  is  possible that the memory gets changed between the times it is sent, so different data can be written to the different devices in the array.  This will be
       detected by check as a mismatch.  However it does not reflect any corruption as the block where this mismatch occurs is being treated by the swap system as being
       empty, and the data will never be read from that block.

       It is conceivable for a similar situation to occur on non-swap files, though it is less likely.

       Thus the mismatch_cnt value can not be interpreted very reliably on RAID1 or RAID10, especially when the device is used for swap.

   BITMAP WRITE-INTENT LOGGING
       From  Linux  2.6.13,  md  supports  a  bitmap  based write-intent log.  If configured, the bitmap is used to record which blocks of the array may be out of sync.
       Before any write request is honoured, md will make sure that the corresponding bit in the log is set.  After a period of time with no writes to an  area  of  the
       array, the corresponding bit will be cleared.

       This bitmap is used for two optimisations.

       Firstly,  after  an unclean shutdown, the resync process will consult the bitmap and only resync those blocks that correspond to bits in the bitmap that are set.
       This can dramatically reduce resync time.

       Secondly, when a drive fails and is removed from the array, md stops clearing bits in the intent log.  If that same drive is  re-added  to  the  array,  md  will
       notice  and  will  only  recover  the  sections  of the drive that are covered by bits in the intent log that are set.  This can allow a device to be temporarily
       removed and reinserted without causing an enormous recovery cost.

       The intent log can be stored in a file on a separate device, or it can be stored near the superblocks of an array which has superblocks.

       It is possible to add an intent log to an active array, or remove an intent log if one is present.

       In 2.6.13, intent bitmaps are only supported with RAID1.  Other levels with redundancy are supported from 2.6.15.

   WRITE-BEHIND
       From Linux 2.6.14, md supports WRITE-BEHIND on RAID1 arrays.

       This allows certain devices in the array to be flagged as write-mostly.  MD will only read from such devices if there is no other option.

       If a write-intent bitmap is also provided, write requests to write-mostly devices will be treated as write-behind requests and md will not  wait  for  writes  to
       those requests to complete before reporting the write as complete to the filesystem.

       This allows for a RAID1 with WRITE-BEHIND to be used to mirror data over a slow link to a remote computer (providing the link isn't too slow).  The extra latency
       of the remote link will not slow down normal operations, but the remote system will still have a reasonably up-to-date copy of all data.

   RESTRIPING
       Restriping, also known as Reshaping, is the processes of re-arranging the data stored in each stripe into a new layout.  This might involve changing  the  number
       of  devices in the array (so the stripes are wider), changing the chunk size (so stripes are deeper or shallower), or changing the arrangement of data and parity
       (possibly changing the raid level, e.g. 1 to 5 or 5 to 6).

       As of Linux 2.6.35, md can reshape a RAID4, RAID5, or RAID6 array to have a different number of devices (more or fewer) and to have a different layout  or  chunk
       size.   It  can  also  convert  between  these different RAID levels.  It can also convert between RAID0 and RAID10, and between RAID0 and RAID4 or RAID5.  Other
       possibilities may follow in future kernels.

       During any stripe process there is a 'critical section' during which live data is being overwritten on disk.  For the  operation  of  increasing  the  number  of
       drives  in  a raid5, this critical section covers the first few stripes (the number being the product of the old and new number of devices).  After this critical
       section is passed, data is only written to areas of the array which no longer hold live data -- the live data has already been located away.

       For a reshape which reduces the number of devices, the 'critical section' is at the end of the reshape process.

       md is not able to ensure data preservation if there is a crash (e.g. power failure) during the critical section.  If md is asked to start an array  which  failed
       during a critical section of restriping, it will fail to start the array.

       To deal with this possibility, a user-space program must

       o   Disable writes to that section of the array (using the sysfs interface),

       o   take a copy of the data somewhere (i.e. make a backup),

       o   allow the process to continue and invalidate the backup and restore write access once the critical section is passed, and

       o   provide for restoring the critical data before restarting the array after a system crash.

       mdadm versions from 2.4 do this for growing a RAID5 array.

       For  operations  that  do  not  change  the  size of the array, like simply increasing chunk size, or converting RAID5 to RAID6 with one extra device, the entire
       process is the critical section.  In this case, the restripe will need to progress in stages, as a section is suspended, backed up, restriped, and released.

   SYSFS INTERFACE
       Each block device appears as a directory in sysfs (which is usually mounted at /sys).  For MD devices, this directory will contain a subdirectory called md which
       contains various files for providing access to information about the array.

       This  interface  is  documented more fully in the file Documentation/md.txt which is distributed with the kernel sources.  That file should be consulted for full
       documentation.  The following are just a selection of attribute files that are available.

       md/sync_speed_min
              This value, if set, overrides the system-wide setting in /proc/sys/dev/raid/speed_limit_min for this array only.  Writing the value system  to  this  file
              will cause the system-wide setting to have effect.

       md/sync_speed_max
              This is the partner of md/sync_speed_min and overrides /proc/sys/dev/raid/speed_limit_max described below.

       md/sync_action
              This  can  be  used  to  monitor and control the resync/recovery process of MD.  In particular, writing "check" here will cause the array to read all data
              block and check that they are consistent (e.g. parity is correct, or all mirror replicas are the same).  Any discrepancies found are NOT corrected.

              A count of problems found will be stored in md/mismatch_count.

              Alternately, "repair" can be written which will cause the same check to be performed, but any errors will be corrected.

              Finally, "idle" can be written to stop the check/repair process.

       md/stripe_cache_size
              This is only available on RAID5 and RAID6.  It records the size (in pages per device) of the  stripe cache which  is  used  for  synchronising  all  write
              operations  to the array and all read operations if the array is degraded.  The default is 256.  Valid values are 17 to 32768.  Increasing this number can
              increase performance in some situations, at some cost in system memory.  Note, setting this value too high can result in an "out of memory" condition  for
              the system.

              memory_consumed = system_page_size * nr_disks * stripe_cache_size

       md/preread_bypass_threshold
              This  is  only  available  on  RAID5 and RAID6.  This variable sets the number of times MD will service a full-stripe-write before servicing a stripe that
              requires some "prereading".  For fairness this defaults to 1.  Valid values are 0 to stripe_cache_size.  Setting  this  to  0  maximizes  sequential-write
              throughput at the cost of fairness to threads doing small or random writes.

   KERNEL PARAMETERS
       The md driver recognised several different kernel parameters.

       raid=noautodetect
              This will disable the normal detection of md arrays that happens at boot time.  If a drive is partitioned with MS-DOS style partitions, then if any of the
              4 main partitions has a partition type of 0xFD, then that partition will normally be inspected to see if it is part of an MD array, and if any full arrays
              are found, they are started.  This kernel parameter disables this behaviour.

       raid=partitionable

       raid=part
              These  are available in 2.6 and later kernels only.  They indicate that autodetected MD arrays should be created as partitionable arrays, with a different
              major device number to the original non-partitionable md arrays.  The device number is listed as mdp in /proc/devices.

       md_mod.start_ro=1

       /sys/module/md_mod/parameters/start_ro
              This tells md to start all arrays in read-only mode.  This is a soft read-only that will automatically switch to read-write on the  first  write  request.
              However until that write request, nothing is written to any device by md, and in particular, no resync or recovery operation is started.

       md_mod.start_dirty_degraded=1

       /sys/module/md_mod/parameters/start_dirty_degraded
              As  mentioned  above,  md  will  not normally start a RAID4, RAID5, or RAID6 that is both dirty and degraded as this situation can imply hidden data loss.
              This can be awkward if the root filesystem is affected.  Using this module parameter allows such arrays  to  be  started  at  boot  time.   It  should  be
              understood that there is a real (though small) risk of data corruption in this situation.

       md=n,dev,dev,...

       md=dn,dev,dev,...
              This  tells  the  md driver to assemble /dev/md n from the listed devices.  It is only necessary to start the device holding the root filesystem this way.
              Other arrays are best started once the system is booted.

              In 2.6 kernels, the d immediately after the = indicates that a partitionable device (e.g.  /dev/md/d0) should be created rather  than  the  original  non-
              partitionable device.

       md=n,l,c,i,dev...
              This tells the md driver to assemble a legacy RAID0 or LINEAR array without a superblock.  n gives the md device number, l gives the level, 0 for RAID0 or
              -1 for LINEAR, c gives the chunk size as a base-2 logarithm offset by twelve, so 0 means 4K, 1 means 8K.  i is ignored (legacy support).

FILES

       /proc/mdstat
              Contains information about the status of currently running array.

       /proc/sys/dev/raid/speed_limit_min
              A readable and writable file that reflects the current "goal" rebuild speed for times when non-rebuild activity is current on an array.  The speed  is  in
              Kibibytes per second, and is a per-device rate, not a per-array rate (which means that an array with more disks will shuffle more data for a given speed).
              The default is 1000.

       /proc/sys/dev/raid/speed_limit_max
              A readable and writable file that reflects the current "goal" rebuild speed for times when no non-rebuild activity is current on an array.  The default is
              200,000.

SEE ALSO

       mdadm(8), mkraid(8).

                                                                                                                                                                   MD(4)
 

Hi, Guest!

This is a manual page collection for Linux and Unix-like operating system.

Features

  • Works with all browsers and mobile phones.
  • The HTML in this layout validates as XHTML 1.0 strict.

Links

Search this site