RAID level 5 recovery

[DanglingPointer]

Hi I will be implementing a RAID 5 and 0 shortly and was wanting to know about recovery from level 5:

What exactly is meant by parity here, and if one disk fails can its whole contents be rebuilt from parity data? How is this possible when only one disk's worth of parity is held...?

 

[comtec17]

Raid Level 5 -
This level is commonly referred to as striping with distributed parity. RAID Level 5 is similar to level 4, but distributes parity among the drives. No single disk is devoted to parity. This can speed small writes in multiprocessing systems. Because parity data must be distributed on each drive during reads, the performance for reads tends to be considerably lower than a level 4 array.


For Raid 0/5 -
RAID 0/5 is a dual level array that utilizes multiple RAID5 sets into a single array. In RAID 0/5 array, a single hard drive failure can occur in each of the RAID5 without any loss of data on the entire array. Keep in mind, as the number of hard drives increase in an array, so too, does the increased possibility of a single hard drive failure. Although there is an increased write performance in RAID 0/5, once a hard drive fails and reconstruction takes place, there is a noticeable decrease in performance, data/program access will be slower, and transfer speeds on the array will be effected.

 

[DanglingPointer]

I know what RAID 5 is - other sites have similar descriptions.

You seem to be saying a whole disk can be reconstructed, how is this possible? Is some sort of compression used?

 

[comtec17]

It uses the parity bits to reconstruct the failed drive. This is why if you lose more than one drive in your RAID 5 you cannot recover.