You can find a full explanation of how RAID 4 and RAID 5 volumes work on our RAID levels page.
Both RAID 4 and RAID 5 volumes give you very high performance while still protecting your volume from disk failure. They are a great choice if you need high performance for writing large files or for reading files of any size, ie for video editing, animation studios, digital photography, prepress and graphic arts. With RAID 4 and RAID 5, the volume will keep working even after a disk gets an error or fails completely.
If you are using SSDs, RAID 4 is preferable to RAID 5; with SSDs, RAID 4 reads are up to 20% quicker, so it's great for things like large video files which need to be read fast.
RAID 4 and RAID 5 are good for reading small files which are frequently read. They are not a good choice if you need to write a lot of small files as fast as possible. If you need to write many small files, we suggest you use RAID 1+0.
With SoftRAID, a RAID volume can have up to 16 disks. For increased reliability, we recommend that you have up to 8 disks in your RAID 4 or RAID 5 volume. If you are using more than 8 disks, we recommend you use RAID 1+0 for increased reliability.
The SoftRAID driver always creates the correct parity information for each block when writing to the volume. The parity information gets written out at the same time that your files are written so it should always be correct.
There are problems with specific Macs which can result in this parity information not being written out correctly. If you want to confirm that all the parity information in your RAID 4 or RAID 5 volume is correct, you can validate your volume. When you validate a RAID 4 or RAID 5 volume, SoftRAID reads each set of blocks and calculates its parity information. It then compares this parity information with what is already stored on the volumes disks. If the parity information does not match, it updates the parity information on the disk. The SoftRAID application displays a count of the number of blocks updated whenever you validate a volume.
Because of the way that RAID 4 and RAID 5 work—by creating parity data, which can be used to rebuild your data, and storing that parity data separately from the data it encodes—one of your RAID 4 or RAID 5 disks can completely stop working and your data is safe.
Read more about how parity data is calculated and stored in RAID 4 and RAID 5 volumes here.