Thanks, Neil. To end this long email thread: what is "more important": update time or event count? Or perhaps they are updated simultaneously? Thanks, Alex. On Thu, Oct 20, 2011 at 1:56 AM, NeilBrown <neilb@xxxxxxx> wrote: > On Wed, 19 Oct 2011 14:01:16 +0200 Alexander Lyakas <alex.bolshoy@xxxxxxxxx> > wrote: > >> Thanks, Neil. >> I experimented with --force switch, and I saw that when using this >> switch it is possible to start the array, even though I am sure that >> the data will be corrupted. Such as selecting stale drives (which have >> been replaced previously etc.) >> Can I have some indication that it is "relatively safe" to start the >> array with --force? >> For example, in the case of "dirty degraded", perhaps it might be >> relatively safe. >> >> What should I look at? The output of --examine? Or something else? > > Yes, look at the output of examine. Look particularly at update time and > event counts, but also at RAID raid level etc and the role in the array > played by each device. > > Then choose the set of devices that you should are most likely to have > current data and given them to "mdadm --assemble --force". > > Obviously if one device hasn't been updated for months, that is probably a > bad choice, while if one device is only a few minutes behind the others, then > that is probably a good choice. > > Normally there isn't much choice to be made, and the answer will be obvious. > But if you let devices fail and leave them lying around, or don't replace > them, then that can cause problems. > > If you need to use --force there might be some corruption. Or there might > be none. And there could be a lot. But mdadm has know way of knowing. > Usually mdadm will do the best that is possible, but it cannot know how good > that is. > > NeilBrown > > > >> >> Thanks, >> Alex. >> >> >> On Wed, Oct 12, 2011 at 5:45 AM, NeilBrown <neilb@xxxxxxx> wrote: >> > On Tue, 11 Oct 2011 15:11:47 +0200 Alexander Lyakas <alex.bolshoy@xxxxxxxxx> >> > wrote: >> > >> >> Hello Neil, >> >> can you please confirm for me something? >> >> In case the array is FAILED (when your enough() function returns 0) - >> >> for example, after simultaneous failure of all drives - then the only >> >> option to try to recover such array is to do: >> >> mdadm --stop >> >> and then attempt >> >> mdadm --assemble >> >> >> >> correct? >> > >> > Yes, though you will probably want a --force as well. >> > >> >> >> >> I did not see any other option to recover such array Incremental >> >> assemble doesn't work in that case, it simply adds back the drives as >> >> spares. >> > >> > In recent version of mdadm it shouldn't add them as spare. It should say >> > that it cannot add it and give up. >> > >> > NeilBrown >> > >> > >> > > > -- 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
