diff options
Diffstat (limited to 'md.4')
| -rw-r--r-- | md.4 | 41 |
1 files changed, 35 insertions, 6 deletions
@@ -16,7 +16,7 @@ Array of Independant Devices. .B md support RAID levels 1 (mirroring) 4 (striped array with parity device) and 5 (striped array with distributed parity information. If a single underlying -device fails while using one of these level, they array will continue +device fails while using one of these level, the array will continue to function. .PP .B md @@ -24,36 +24,65 @@ also supports a number of pseudo RAID (non-redundant) configuations including RAID0 (striped array), LINEAR (catenated array) and MULTIPATH (a set of different interfaces to the same device). -.SS RAID SUPER BLOCK +.SS MD SUPER BLOCK With the exception of Legacy Arrays described below, each device that is incorportated into an MD array has a .I super block written towards the end of the device. This superblock records information about the structure and state of the array so that the -array an be reliably re-assembled after a shutdown. +array can be reliably re-assembled after a shutdown. The superblock is 4K long and is written into a 64K aligned block that -start at least 64K and less than 128K from the end of the device +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 ammount of space before the +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. The superblock contains, among other things: .TP LEVEL -The +The manner in which the devices are arranged into the array +(linear, raid0, raid1, raid4, raid5, multipath). .TP UUID a 128 bit Universally Unique Identifier that identifies the array that this device is part of. +.SS LEGACY ARRAYS +Early versions of the +.B md +driver only supported Linear and Raid0 configurations and so +did not use an MD superblock (as there is not state that needs to be +recorded). While it is strongly recommended that all newly created +arrays utilise a superblock to help ensure that they are assembled +properly, the +.B md +driver still supports legacy linear and raid0 md arrays that +do not have a superblock. + .SS LINEAR + +A linear array simply catenates the available space on each +drive together 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 and so the array is made bigger without disturbing the +data that is on the array. However this cannot be done on a live +array. + + + .SS RAID0 + +A RAID0 array (which has zero redundancy) is also known as a +striped array. .SS RAID1 .SS RAID4 .SS RAID5 +.SS MUTIPATH .SS REBUILD/RESYNC .SH FILES .TP |