Problem Solving | MediaVault 4105 User Manual |
TABLE 7-2. Frequently Asked Questions.
What is RAID 3? | In RAID 3, all of the drives except one (this one called a parity |
| drive) are striped in RAID 0, as above. |
| However this one drive has a special purpose: Through a |
| simple mathematical calculation, it is able to operate if one of |
| the RAID 0 drives goes down. |
| If, for example, you set a rule that all of the bits (like switches - |
| on/off) on all of the drive have to add up to an odd number, |
| such as 0111 (with 1 being on, 0 being off), the extra drive |
| stores the extra piece of data necessary to keep this number |
| odd. In the case of 0111, the 5th bit would be 0, so that |
| 0+1+1+1+0 = 3 (which is odd). |
| If one of any of the bits is lost, suppose the 2nd one: 0?110, |
| by using the same rule (all numbers must add up to an odd |
| number), it is possible to calculate the missing number: |
| 0+?+1+1+0=2 (which is even), so the missing number must |
| be 1 in order to make that formula add up to an odd. |
| To do RAID 3 requires a minimum of 3 disks - the MV 4105 |
| uses one set of 5 (The reason you couldn't use two disks is |
| that you would be mirroring, with the 2nd drive in the mirror |
| being the inverted version of the first). |
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What is RAID 5? | RAID 5 is the same as RAID 3, except instead of having a |
| dedicated parity drive, the parity is distributed across all of the |
| disks, alternating disks in order. |
| In the first strip of sectors (i.e. sector 0 of all of the drives), the |
| 5th drive would have the parity, then on the 2nd strip (sector 1 |
| of all drives), drive 1 would have parity, then drive 2, etc. |
| RAID 5 requires a minimum of 3 drives - the MV 4105 does |
| not support RAID 5 - only RAID 3 |
| (The drawbacks with RAID 5 is that additional calculation for |
| the location of the parity within a strip |
| have to be |
| performance goes down as well). |
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MV 4105_Ciprico Inc. |
