I know that RAID5 is very appealing 'cause you end with 'a lot of usable disk space' but, I always discourage to use it.Each chunk of data to be written to disk is divided in Numer of physical RAID disks writes - 1 plus another write to store CRC on to the remaining disk ( the CRC chunk is written in a round-robin model using all RAID disks ). For write changed data, the RAID logic must locate where the data was, rewrite it and calculate the changes to the parity to reflect the changes Another important point is the time spend on rebuild a previously failed disk ( data is not copied from antoher disk, is regenerated using the data in CRC chunks ) And another tip, If fails 2 disks, good by data, must restore from backup
How about raid 6? With raid 6 you can loose 2 disks and you loose nothing. I have around 10TB mostly on raid 6 using 250GB and 330 GB SATA drives and they work great. I have had to replace a disk from time to time but I have never had 2 go bad at once. Always try to use any more 'friendly' RAID as RAID1 / RAID10
But then you throw away 1/2 the space.
John
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