RAID cấp độ 5 is similarto striping, but with parity data distributed across all components (diskor logical volume). If a component fails, the data on the failed componentcan be rebuilt from the distributed data and parity information on the othercomponents. In Solaris Volume Manager, a RAID 5 volume is avolume that supports RAID level 5.
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A RAID 5 volume uses storage capađô thị equivalent khổng lồ one component inthe volume khổng lồ store redundant information (parity) about user data storedon the remainder of the RAID 5 volume"s components. That is, if you have threecomponents, the equivalent of one will be used for the parity information.If you have five sầu components, then the equivalent of one will be used for parityinformation. The parity is distributed across all components in the volume.Like a mirror, a RAID 5 volume increases data availability, but with a minimumof cost in terms of hardware and only a moderate penalty for write operations.However, you cannot use a RAID 5 volume for root (/), /usr, and swap, or for existing tệp tin systems.
Solaris Volume Manager automatically resynchronizes a RAID 5 volume whenyou replace an existing component. Solaris Volume Manager also resynchronizes RAID5 volumes during rebooting if a system failure or panic took place.
Example—RAID 5 Volume
Figure 14–1 shows a RAID 5 volume, d40.
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The first three data chunks are written khổng lồ Disks A through C. The nextchunk that is written is a parity chunk, written to Drive D, which consistsof an exclusive OR of the first three chunks of data. This pattern of writingdata & parity chunks results in both data và parity being spread acrossall disks in the RAID 5 volume. Each drive sầu can be read independently. Theparity protects against a single disk failure. If each disk in this examplewere 2 Gbytes, the total capacity of d40 would be 6 Gbytes.(One drive"s worth of space is allocated to parity.)
Figure 14–1 RAID 5 Volume Example
Example—Concatenated (Expanded)RAID 5 Volume
The followingfigure shows an example of an RAID 5 volume that initially consisted of fourdisks (components). A fifth disk has been dynamically concatenated lớn thevolume lớn expvà the RAID 5 volume.
Figure 14–2 Expanded RAID 5 Volume Example
The parity areas areallocated when the initial RAID 5 volume is created. One component"s worthof space is allocated khổng lồ parity, although the actual parity blocks are distributedacross all of the original components lớn distribute I/O. When you concatenateadditional components lớn the RAID, the additional space is devoted entirelyto lớn data. No new parity blocks are allocated. The data on the concatenatedcomponents is, however, included in the parity calculations, so it is protectedagainst single device failures.
Concatenated RAID 5 volumes are not suited for long-term use. Use aconcatenated RAID 5 volume until it is possible lớn reconfigure a larger RAID5 volume & copy the data khổng lồ the larger volume.
lưu ý –When you add a new component khổng lồ a RAID 5 volume, Solaris Volume Manager “zeros”all the blocks in that component. This process ensures that the parity willprotect the new data. As data is written to the additional space, Solaris Volume Manager includesit in the parity calculations.