diff options
Diffstat (limited to 'md.man')
| -rw-r--r-- | md.man | 42 |
1 files changed, 35 insertions, 7 deletions
@@ -19,8 +19,8 @@ DDEESSCCRRIIPPTTIIOONN mmdd support RAID levels 1 (mirroring) 4 (striped array with parity device) and 5 (striped array with distributed par- ity information. If a single underlying device fails - while using one of these level, they array will continue - to function. + while using one of these level, the array will continue to + function. mmdd also supports a number of pseudo RAID (non-redundant) configuations including RAID0 (striped array), LINEAR @@ -28,36 +28,64 @@ DDEESSCCRRIIPPTTIIOONN faces to the same device). - RRAAIIDD SSUUPPEERR BBLLOOCCKK + MMDD SSUUPPEERR BBLLOOCCKK With the exception of Legacy Arrays described below, each device that is incorportated into an MD array has a _s_u_p_e_r _b_l_o_c_k 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- + state of the array so that the 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 + 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 ammount of space before the super block, so + 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: - LEVEL The + LEVEL The manner in which the devices are arranged into + the array (linear, raid0, raid1, raid4, raid5, mul- + tipath). UUID a 128 bit Universally Unique Identifier that iden- tifies the array that this device is part of. + LLEEGGAACCYY AARRRRAAYYSS + Early versions of the mmdd 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 assem- + bled properly, the mmdd driver still supports legacy linear + and raid0 md arrays that do not have a superblock. + + LLIINNEEAARR + 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. + + + + RRAAIIDD00 + A RAID0 array (which has zero redundancy) is also known as + a striped array. + RRAAIIDD11 RRAAIIDD44 RRAAIIDD55 + MMUUTTIIPPAATTHH RREEBBUUIILLDD//RREESSYYNNCC FFIILLEESS //pprroocc//mmddssttaatt |