On Thu, May 10, 2012 at 8:59 AM, David Brown <david.brown@xxxxxxxxxxxx> wrote: > (I accidentally sent my first reply directly to the OP, and forgot the > mailing list - I'm adding it back now, because I don't want the OP to follow > my advice until others have confirmed or corrected it!) > Thanks. I just hit reply all and did not notice that... > > On 09/05/2012 21:53, Patrik Horník wrote: >> Great suggestion, thanks. >> >> So I guess steps with exact parameters should be: >> 1, add spare S to RAID5 array >> 2, mdadm --grow /dev/mdX --level 6 --raid-devices N+1 --layout=preserve >> 3, remove faulty drive and add replacement, let it synchronize >> 4, possibly remove added spare S >> 5, mdadm --grow /dev/mdX --level 5 --raid-devices N > > > Yes, that's what I was thinking. You are missing "2b - let it synchronise". > > Of course, another possibility is that if you have the space in the system > for another drive, you may want to convert to a full raid6 for the future. > That way you have the extra safety built-in in advance. But that will > definitely lead to a re-shape. > > >> >> My questions: >> - Are you sure steps 3, 4 and 5 would not cause reshaping? > > I /believe/ it will avoid a reshape, but I can't say I'm sure. This is > stuff that I only know about in theory, and have not tried in practice. > > >> >> - My array has now left-symmetric layout, so after migration to RAID6 >> it should be left-symmetric-6. Is RAID6 working without problem in >> degraded mode with this layout, no matter which one or two drives are >> missing? >> > > The layout will not affect the redundancy or the features of the raid - it > will only (slightly) affect the speed of some operations. > > >> - What happens in step 5 and how long does it take? (If it is without >> reshaping, it should only upgrade superblocks and thats it.) > > That is my understanding. > > >> >> - What happens if I dont remove spare S before migration back to >> RAID5? Will the array be reshaped and which drive will it make into >> spare? (If step 5 is instantaneous, there is no reason for that. But >> if it takes time, it is probably safer.) >> > > I /think/ that the extra disk will turn into a hot spare. But I am getting > out of my depth here - it all depends on how the disks get numbered and how > that affects the layout, and I don't know the details here. > > >> So all and alll, what guys do you think is more reliable now, new >> hot-replace or these steps? > > > I too am very curious to hear opinions. Hot-replace will certainly be much > simpler and faster than these sorts of re-shaping - it's exactly the sort of > situation the feature was designed for. But I don't know if it is > considered stable and well-tested, or "bleeding edge". > > mvh., > > David > > > >> >> Thanks. >> >> Patrik >> >> On Wed, May 9, 2012 at 8:09 AM, David Brown<david.brown@xxxxxxxxxxxx> >> wrote: >>> On 08/05/12 11:10, Patrik Horník wrote: >>>> >>>> Hello guys, >>>> >>>> I need to replace drive in big production RAID5 array and I am >>>> thinking about using new hot-replace feature added in kernel 3.3. >>>> >>>> Does someone have experience with it on big RAID5 arrays? Mine is 7 * >>>> 1.5 TB. What do you think about its status / stability / reliability? >>>> Do you recommend it on production data? >>>> >>>> Thanks. >>>> >>> >>> If you don't want to play with the "bleeding edge" features, you could >>> add >>> the disk and extend the array to RAID6, then remove the old drive. I >>> think >>> if you want to do it all without doing any re-shapes, however, then you'd >>> need a third drive (the extra drive could easily be an external USB disk >>> if >>> needed - it will only be used for writing, and not for reading unless >>> there's another disk failure). Start by adding the extra drive as a hot >>> spare, then re-shape your raid5 to raid6 in raid5+extra parity layout. >>> Then >>> fail and remove the old drive. Put the new drive into the box and add it >>> as >>> a hot spare. It should automatically take its place in the raid5, >>> replacing >>> the old one. Once it has been rebuilt, you can fail and remove the extra >>> drive, then re-shape back to raid5. >>> >>> If things go horribly wrong, the external drive gives you your parity >>> protection. >>> >>> Of course, don't follow this plan until others here have commented on it, >>> and either corrected or approved it. >>> >>> And make sure you have a good backup no matter what you decide to do. >>> >>> mvh., >>> >>> David >>> >> >> > -- 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
