On 2013-07-02 18:53, Nick Holland wrote: > On 07/02/13 17:07, Jean-Francois Simon wrote: > > Le 20/05/2013 13:46, Nick Holland a écrit : > >> On 05/20/13 00:52, Hugo Osvaldo Barrera wrote: > ... > >>> 3) The man pages report RAID5 as experimental. I'm curious, why > >>> is this so? Is it just not-very-thoroughly tested, or is there > >>> some missing feature? I read on a 2010 presentation that rebuild > >>> was not implemented yet, is this still so? > >> That's really a question you will need to find out though > >> experimentation before you implement (i.e., you MUST practice this > >> recovery stuff before going into production), but yes, RAID5 > >> rebuild is still not there, so I would NOT recommend going this > >> route. > >> > >> However, a nice little RAID1 system to start, hopefully leaving you > >> two SATA ports for the next generation/upgrade disks. > >> > >> Nick. > > > > "RAID5 rebuild is still not there" Can you please make it more clear > > what actual state of soft raid can and what it cannot do under RAID 5 > > ... I'm not so sure to get it, thank you. > > > > J.-F. > > > > "RAID5 rebuild is still not there" -> there's no RAID5 rebuild. I'm not > sure how to make it more clear... > > Ok, let's try this... > Today, you take four 1TB disks, and make a 3TB RAID5 volume. You can do > that. Works great. > > Now, a lot of people might call this "Job Done". Not me. The point of > RAID isn't to build complicated systems, but to have the system keep > your butt out of the fire when things go wrong. > > Next month, one of those drive fail. That's ok, RAID5 is designed to > keep your data usable with one drive down. THAT is the point of RAID. > > You pat yourself on the back and say, "I'm glad I am using RAID5". > You replace the failed drive and... > ... > um... now what? > You have a three drive degraded RAID5 system with no remaining > redundancy...and a new drive that is currently unused. You have no > ability to rebuild the function of the failed drive into the new > drive...because the RAID5 rebuild is not there. > > Oh, poo. > > Your options? Well, > * you can build a NEW array on other disks (hope you have enough ports > to plug them into), copy the data from the old one to the new one > * you can hope your backup system is perfect, and rebuild the entire > array and reload from backup > * you can hope a second drive doesn't fail in your array... for the life > of the system. > > Not much else I can think of. > > If you want to play with softraid and raid5, hey, have a blast. You > want to put critical data on it? I'd not suggest that. A job ago, I > had some relatively large chunks of data to hash through to find some > needles of data in and no disks handy that could do it in one > chunk...but I had some big disk array boxes, and a lot of smallish SCSI > disks I could stick in them (and the office space was really cold, so a > bit of heat under my desk was not unappreciated). I think I did them as > softraid RAID0, but I could have done it as RAID5 with this system -- > the data is there just for analysis, not storage. RAID5 might give me a > few minutes to pull data off that I realized was important only after > the drive failed, but otherwise the loss of data on this array would not > have been catastrophic at all. > > Now, anyone who drops important data on any kind of RAID system without > figuring out how to deal with disk (and controller) failures deserves > what they get. So if I was a nice guy, I'd have said "Go try it out on > some spare hardware and unimportant data and answer your own question", > but being the evil bastard that I am, I'm denying you a very important > learning experience. > > Nick. >
Indeed! I wanted to make sure I'd know how to rebuild the RAID after it failed, and that was my initial doubt. You can be pretty much assured that I didn't use RAID5 in the end (I don't have anywhere to copy all my stuff while I rebuild the array). I'm wondering though; is it *so* hard to implement the rebuildage, or is there simply no interest on behalf of the devs? -- Hugo Osvaldo Barrera [demime 1.01d removed an attachment of type application/pgp-signature]
