I am about to replace an old hardware RAID5 array with a Linux software RAID1 array. I was talking to a friend and he claimed that RAID5 was more robust than RAID1.

His claim was that with RAID5, on read the parity data was read to make sure that all the drives were returning the correct data. He further claimed that on RAID1 errors occurring on a drive will go unnoticed because no such checking is done with RAID1.

I can see how this could be true, but can also see that it all depends on how the RAID systems in question are implemented. Surely a RAID5 system doesn't have to read and check the parity data on a read and a RAID1 system could just as easily read from all drives on read to check they were all holding the same data and therefore achieve the same level of robustness (with a corresponding loss of performance).

So the question is, what do RAID5/RAID1 systems in the real world actually do ? Do RAID5 systems check the parity data on reads ? Are there RAID1 systems that read from all drives and compare the data on read ?

See also:

http://serverfault.com/questions/47458/is-raid5-more-robust-than-raid1