Am 11.08.10 00:40, schrieb Peter Taps: > Hi, > > I am going through understanding the fundamentals of raidz. From the man > pages, a raidz configuration of P disks and N parity provides (P-N)*X storage > space where X is the size of the disk. For example, if I have 3 disks of 10G > each and I configure it with raidz1, I will have 20G of usable storage. In > addition, I continue to work even if 1 disk fails. > > First, I don't understand why parity takes so much space. From what I know > about parity, there is typically one parity bit per byte. Therefore, the > parity should be taking 1/8 of storage, not 1/3 of storage. What am I missing? > > Second, if one disk fails, how is my lost data reconstructed? There is no > duplicate data as this is not a mirrored configuration. Somehow, there should > be enough information in the parity disk to reconstruct the lost data. How is > this possible? > > Thank you in advance for your help. > Nah it is more like Disk3 is disk2 xor disk1. You can read about it on Raid5 (raidz is more complicated but the basic idea stays the same). The parity you describe is only for error checking. More like a zfs checksum which also one takes very little additional space.
Arne
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