<\/span>Choosing RAID for Performance<\/span><\/h3>\nThe table below explains different RAID levels and how they impact on performance:<\/p>\n\n
\n\n\n\t| RAID Level<\/th> | Advantages<\/th> | Disadvantages <\/th>\n<\/tr>\n<\/thead>\n |
\n\n\t| RAID level 0 \u2013 Striping<\/td> | RAID 0 offers great performance, both in read and write operations. There is no overhead caused by parity controls.RAID 0 offers great performance, both in read and write operations.
\nAll storage capacity is used, there is no overhead.<\/td> | RAID 0 is not fault-tolerant. If one drive fails, all data in the RAID 0 array are lost. It should not be used for mission-critical systems.<\/td>\n<\/tr>\n |
\n\t| RAID level 1 \u2013 Mirroring<\/td> | RAID 1 offers excellent read speed and a write-speed that is comparable to that of a single drive. In case a drive fails, data do not have to be rebuild, they just have to be copied to the replacement drive.<\/td> | Software RAID 1 solutions do not always allow a hot swap of a failed drive. That means the failed drive can only be replaced after powering down the computer it is attached to. For servers that are used simultaneously by many people, this may not be acceptable. Such systems typically use hardware controllers that do support hot swapping. The main disadvantage is that the effective storage capacity is only half of the total drive capacity because all data get written twice.<\/td>\n<\/tr>\n |
\n\t| RAID level 5<\/td> | Read data transactions are very fast while write data transactions are somewhat slower (due to the parity that has to be calculated). If a drive fails, you still have access to all data, even while the failed drive is being replaced and the storage controller rebuilds the data on the new drive.<\/td> | Technology complexity - If one of the disks in an array using 4TB disks fails and is replaced, restoring the data (the rebuild time) may take a day or longer, depending on the load on the array and the speed of the controller. If another disk goes bad during that time, data are lost forever.<\/td>\n<\/tr>\n |
\n\t| RAID level 6 \u2013 Striping with double parity<\/td> | READs are very fast, If two drives fail, you still have access to all data, even while the failed drives are being replaced. So RAID 6 is more secure than RAID 5.<\/td> | Technology complexity - Rebuilding an array in which one drive failed can take a long time. Write data transactions are slower than RAID 5 due to the additional parity data that have to be calculated. In one report I read the write performance was 20% lower.<\/td>\n<\/tr>\n |
\n\t| RAID level 10 \u2013 combining RAID 1 & RAID 0<\/td> | High Performance and Fault Tolerant - If something goes wrong, All we need to do is copying all the data from the surviving mirror to a new drive. <\/td> | Highly expensive - Half of the storage capacity goes directly for mirroring. <\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n\n- Use NCQ with a long queue.<\/li>\n
- Use\u00a0CFQ scheduler for HDD.\n
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