-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Robert Johnston Sent: Thursday, April 21, 2005 7:14 PM To: MagicITX; Discussion about mythtv Subject: Re: [mythtv-users] INFO: RAID comparison for MythTV
> Incorrect. As RAID5 uses drives in sets of 3 (2 data + 1 CRC), then > you have to lose 2/3rds of the drives in the array for it to fail. > With just 3 drives, that means if 2 of the 3 drives fail, the array is > hosed. With 6 drives, that means 4 of those 6 have to fail, and so on. > Generally with RAID5 arrays that aren't a multiple of 3 (14-drive, > say), the array is configured with 12 drives in the array, and 2 > drives as "Hot Spares" that are swapped in automatically if any one > drive fails. RAID5 means striped data with striped parity. It is not based on a 2 data, 1 CRC system. This is just the minimum amount of drive you need to create one. You can have any amount of drives greater than 2 in a RAID5. If you have a 14 disk RAID5, data is striped across all 14 disks. If you lose any drive, then the system will recover the missing information from the drive through parity. If you lose a 2nd drive, there is no parity information to recover the data from. The idea of 2 data + 1 CRC may work for a 3 disk RAID5, but does not work for any other. If a RAID5 loses a disk when it is reduced (1 drive already failed), then you've lost all of your data. In general you'd have to have 2 complete physical failures to lose all of your data. Because it's always possible to re-assemble the raid and recover data from the parts of the disk that are not destroyed (bad sectors, etc).
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