A RAID5 volume uses storage capacity equivalent to one slice in the volume to store redundant information about user data stored on the remainder of the RAID5 volume's slices. The redundant information is distributed across all slices in the volume. Like a mirror, a RAID5 volume increases data availability, but with a minimum of cost in terms of hardware.
The system must contain at least three state database replicas before you can create RAID5 volumes.
A RAID5 volume can only handle a single slice failure.
Follow the 20-percent rule when creating a RAID5 volume: because of the complexity of parity calculations, volumes with greater than about 20 percent writes should probably not be RAID5 volumes. If data redundancy is needed, consider mirroring.
There are drawbacks to a slice-heavy RAID5 volume: the more slices a RAID5 volume contains, the longer read and write operations will take if a slice fails.
A RAID5 volume must consist of at least three slices. A RAID5 volume can be grown by concatenating additional slices to the volume. The new slices do not store parity information, however they are parity protected. The resulting RAID5 volume continues to handle a single slice failure.
The interlace value is key to RAID5 performance. It is configurable at the time the volume is created; thereafter, the value cannot be modified. The default interlace value is 16 Kbytes. This is reasonable for most applications.
Use the same size disk slices. Creating a RAID5 volume from different size slices results in unused disk space in the volume.
Do not create a RAID5 volume from a slice that contains an existing file system. Doing so will erase the data during the RAID5 initialization process.
RAID5 volumes cannot be striped, concatenated, or mirrored.
# metainit d3 -r c1t4d0s7 c2t4d0s7 c1t5d0s7 d3: RAID is setup
Let's explain the details of the above example. The RAID5 volume d3 is created with the -r option from three slices. Because no interlace is specified, d3 uses the default of 16 Kbytes. The system verifies that the RAID5 volume has been set up, and begins initializing the volume.
# metastat d3 d3: RAID State: Initializing Initialization in progress: 32.0% done Interlace: 32 blocks Size: 35331849 blocks (16 GB) Original device: Size: 35334720 blocks (16 GB) Device Start Block Dbase State Reloc Hot Spare c1t4d0s7 11103 Yes Initializing Yes c2t4d0s7 11103 Yes Initializing Yes c1t5d0s7 11103 Yes Initializing Yes Device Relocation Information: Device Reloc Device ID c1t4d0 Yes id1,sd@SSEAGATE_ST39102LCSUN9.0GLJP248260000194511NU c2t4d0 Yes id1,sd@SSEAGATE_ST39102LCSUN9.0GLJP1841500002945H5FE c1t5d0 Yes id1,sd@SSEAGATE_ST39102LCSUN9.0GLJE34597000029290C8N
When the disks within the RAID5 volume are completed with their initialization phase, this is what it will look like:
# metastat d3 d3: RAID State: Okay Interlace: 32 blocks Size: 35331849 blocks (16 GB) Original device: Size: 35334720 blocks (16 GB) Device Start Block Dbase State Reloc Hot Spare c1t4d0s7 11103 Yes Okay Yes c2t4d0s7 11103 Yes Okay Yes c1t5d0s7 11103 Yes Okay Yes Device Relocation Information: Device Reloc Device ID c1t4d0 Yes id1,sd@SSEAGATE_ST39102LCSUN9.0GLJP248260000194511NU c2t4d0 Yes id1,sd@SSEAGATE_ST39102LCSUN9.0GLJP1841500002945H5FE c1t5d0 Yes id1,sd@SSEAGATE_ST39102LCSUN9.0GLJE34597000029290C8N
# newfs -i 8192 /dev/md/rdsk/d3 newfs: construct a new file system /dev/md/rdsk/d3: (y/n)? y Warning: 1 sector(s) in last cylinder unallocated /dev/md/rdsk/d3: 35331848 sectors in 9839 cylinders of 27 tracks, 133 sectors 17251.9MB in 615 cyl groups (16 c/g, 28.05MB/g, 3392 i/g) super-block backups (for fsck -F ufs -o b=#) at: 32, 57632, 115232, 172832, 230432, 288032, 345632, 403232, 460832, 518432, Initializing cylinder groups: ............ super-block backups for last 10 cylinder groups at: 34765088, 34822688, 34880288, 34933280, 34990880, 35048480, 35106080, 35163680, 35221280, 35278880,
# mkdir /db3 # mount -F ufs /dev/md/dsk/d3 /db3
/dev/md/dsk/d3 /dev/md/rdsk/d3 /db3 ufs 2 yes -
Creating Volumes - (Using Solaris 9 Volume Manager Commands)
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