2009/12/9 Michael Evans <mjevans1983@xxxxxxxxx>: > On Tue, Dec 8, 2009 at 6:03 AM, hank peng <pengxihan@xxxxxxxxx> wrote: >> 2009/12/8 Robin Hill <robin@xxxxxxxxxxxxxxx>: >>> On Tue Dec 08, 2009 at 09:49:48PM +0800, hank peng wrote: >>> >>>> 2009/12/8 Robin Hill <robin@xxxxxxxxxxxxxxx>: >>>> > On Tue Dec 08, 2009 at 09:01:23PM +0800, hank peng wrote: >>>> > >>>> >> Hi, all: >>>> >> As we know, when a raid5 array is created, recovery will be going on >>>> >> which involves some read, one xor and one write. Since there is no >>>> >> real data in the disk at the time, besides, if I am willing to wait >>>> >> for recovery to complete and then use this raid5, how about adding >>>> >> support for a fast recovery method? Right now, what is in my mind is >>>> >> zero all disks which belong to this raid5. I think it will increase >>>> >> raid5 recovery speed when created and decrease CPU usage, since all >>>> >> zero is also XORed. >>>> >> What do raid developers think? >>>> >> >>>> > It'll decrease CPU usage but increase I/O - you're now needing to write >>>> > to all disks. Most systems will be I/O limited rather than CPU limited, >>>> > so the current approach works better. If you want to zero the disks >>>> > then do this before creating the array - you can then use --assume-clean >>>> > to skip the resync process. >>>> > >>>> I think --assume-clean is used mostly when doing performance test and >>>> can't be used when creating a raid5 array using new disk, because >>>> later read and write operation make assumption that all stripe is >>>> XORed. Correct me if I am wrong. >>>> >>> You're correct - that's why I said to zero all the disks first so the >>> XOR data is all correct. >>> >> I think this function is better to be implemented in kernel raid >> layer, not in user space(for example using dd command). >> In this way, we can get good performance and lower cpu usage, also, we >> can make this function be part of raid code so that it can be managed >> by mdadm >>> Cheers, >>> Robin >>> -- >>> ___ >>> ( ' } | Robin Hill <robin@xxxxxxxxxxxxxxx> | >>> / / ) | Little Jim says .... | >>> // !! | "He fallen in de water !!" | >>> >> >> >> >> -- >> The simplest is not all best but the best is surely the simplest! >> -- >> 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 >> > > How about documenting this better? 'zeroing all underlying devices > then creating with --assume-clean' will be clean because the parity > algorithm is even (or similar to 'even parity')? > -- Yes, that's what I am thinking. I think it is better to implement this function in kernel's md layer. I wonder what Neil Brown think of this? > 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 > -- The simplest is not all best but the best is surely the simplest! -- 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
