RE: General RAID5 question - dangers?

From: William Rice <ricew@operamail.com> > >I will admit to having some fear of RAID 5 but for different reasons. I >like >being >able to lose 3 or 4 disks and still have at least a chance of not having to >restore my data. This is mainly because I am a lazy bum who does That is a major plus of RAID10. >not like the idea of doing work which I do not have to. I am interested >in the theory that due to the fact that parity is calculated it is more >susceptible >to error. Would you mind adding a little more meat to that argument, or >is it based on more complex=more problems? Or maybe he fact that it >reads all the other disks to get the information to change the parity so >there is more oppurtunity for a problem? Well, any calculation or process is an opportunity to introduce errors. I'm sure the vendors cope with the resilience issues in a number of different ways, with greater or lesser success. However, another issue is that RAID3/4/5 require greater load on the disk devices. If I read from a RAID10, I only hit the disks I need. If I read from RAID5, every disk in the stripe gets hit for every read. This increases the work on the disk, which in itself leads to quicker failure. But to me, it's all academic. Saving money on disk is silly, and if people like Art (and my most recent .com customer) migrate away from RAID3/4/5 to RAID10 (and Art manages more than 7TB of disk!!) because of the pain it causes, and despite the cost "savings" that's a good enough endorsement for me. I've seen a RAID5 let go, completely without warning. We knew the disks were blown before the RAID did. We were just exceptionally lucky that we didn't lose absolutely everything. This is not to say that RAID10 can't fail, *anything* can fail, but the margin for failure is so much lower with RAID10 than RAID5 that I feel much happier with the risk. >I have never been priveleged enough to witness a site using RAID 5 have >serious issues, and am trying to understand where mirroring would help >in such a situation Well, if that's your idea of a privilege, can I interest you in the privilege of cleaning my house out every week for free? :-) ________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com