On Sun, 31 Oct 2010 14:19:13 +0000 John Robinson <john.robinson@xxxxxxxxxxxxxxxx> wrote: > On 31/10/2010 13:41, Florian Dazinger wrote: > [...] > > Unlike what I excpected from the man-page, > > I had network traffic during the *whole* reshape-process, not just at > > the beginning. > > Perhaps the man page needs updating then. The backup file is only used > at the beginning for grows, or at the end for shrinks, but a same-size > reshape (as yours was, going from 4-disc RAID-6 to 3-disc RAID-5) needs > to back up everything because there's no spare space. > > Of course when the man page section on reshaping and the use of the > backup file was originally written, changing RAID level wasn't > supported, and nor were shrinks, so the backup file was only used for > grows, so it was only used at the beginning. > > If I've got the above right (someone please correct me if I'm not) > perhaps I could make a modest contribution (for a change) by updating/ > patching the man page... That would certainly be appreciated. Your understanding appear to be correct! > > Actually that makes me wonder: the man page says spare devices can be > used for the backup if there are any. Is that still true with all the > grows, shrinks and level-changing reshape options we have now? I'd > expect that method of backup to be (slightly) faster than putting the > backup on a filesystem (even on a local disc). I think mdadm insists on a backup file for shrinks and same-size transformations. It probably could use a spare, but I think there is generally less likely to be one - when you are growing an array there is almost certainly an array to grow to. Write to a file on a local disk should be just as fast as writing to a raw device .... I guess there could be a little bit of filesystem overhead, but I doubt you would be able to measure it. > > > thank you very much for all the good work and user support on this list!! > > It is nice to hear positive feedback, but at the same time I tend to > think that since there must be millions of users of md/mdadm, it's > pretty encouraging that there are only one or two "arghs" per day... :-) Certainly - positive feedback is always welcome! NeilBrown > > Cheers, > > John. > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
