Jakob, thank you very much for your prompt, quick answer, you sorted out most of the questions I had. > -----Original Message----- > From: linux-raid-owner@vger.kernel.org [mailto:linux-raid- > owner@vger.kernel.org] On Behalf Of Jakob &PSgr;stergaard > Sent: Tuesday, February 05, 2002 10:28 PM > To: Cajoline > Cc: linux-raid@vger.kernel.org > Subject: Re: raidreconf > > On Tue, Feb 05, 2002 at 06:51:46PM +0200, Cajoline wrote: > > Hi. > ... > > As for relocating the drives, someone told me that just moving them > > along the new ide slots so the initial device sequence (that I used in > > the raidtab when I mkraid'ed) is preserved would be enough for that > > matter. However, I'm afraid that's not right. This is the first > > question. > > If you use persistent superblocks, the RAID layer will figure out by > itself when you move the disks. The superblock will contain the > data telling "this partition is number X in the array". So you should > be safe there. So this means I have to maintain the device sequence in the new arrangement, right? I hope this doesn't sound too naive, but how will the raid layer know the new location of each partition? > > Apart from the possible problems one may come across with raidreconf, as > > warned by the authors, I also read that raidreconf will take a > > considerable amount of time to complete the conversion, so if there is a > > way to do the relocation without using raidreconf, I would prefer it, to > > stay on the safe side. > > Yes, raidreconf runs can be fairly time consuming. A chunk-size > conversion on > a 40-60 GB RAID-0 can take several hours. It all depends very much on the > amount of memory in the machine - raidreconf will make generous use of > whatever > RAM you have in the machine, but converting 100's of GB arrays on a 32 MB > box > is going to be very time consuming (I did the 40 GB 32->64K chunk-size > (RAID-0) > conversion on a 48 MB box, and I think it took around 4 or 6 hours - but > that > was a silly experiment really). I decided to do a test tonight with a few drives I could repartition just for this. I used two drives, 80gb and 100gb, made two equal-size partitions on each, and made an array with the 2 40gb and the 1 50gb partition. I copied something to it, filled about 1.5gb, and then tried raidreconf to add the second 50gb partition to the array. The box had 224mb RAM and a Duron 850 MHz processor. It gave an estimate of about 12 hours to complete the process. I let it continue for about 2 hours before I aborted, and it hadn't reached 20% yet. I am not sure how much memory it used, unfortunately I just didn't look. Is this estimation accurate or close to accurate? So could I assume that adding a 100gb disk to a 380gb array would take a multiple of that time to complete, perhaps more than 48 hours? > On RAID-0, I don't know of any other way than using raidreconf for adding > disks. You could, however, create a new linear array over your existing > array and the new disk. With a little care, some -f options for mkraid, > and a following ext2resize, it should be quite possible (and safe if you > do not make mistakes and do not have a power outage... ;) I suppose I can't make a RAID-0 array that consists of the existing array and the new disk and still preserve the existing filesystem, since the striping might overwrite the fs, right? Can you be a little more specific as to what I should take special care for in this process? I am not sure I got it right, but I don't know if/how the resize utility will be able find the filesystem that was running on top of the old md0 under the new linear-raid device. > (On a related note: raidreconf is rather sensitive to power outages - it > does not currently keep a journal or log over moved blocks, so there is > currently no way to recover data if the reconfiguration is halted) Yes I know, it's one of the reasons I hesitate to use raidreconf, along with the other problem, that I'm not sure I can keep the box offline (with the raid stopped) long enough for raidreconf to finish its' job. Thank you again. This has been a big help for me to decide what to do in this situation. Regards, Cajoline Leblanc cajoline at chaosengine dot de - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
