From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brown Subject: Re: Hot-replace for RAID5 Date: Thu, 10 May 2012 08:59:36 +0200 Message-ID: <4FAB6758.5050109@hesbynett.no> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: patrik@dsl.sk Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids (I accidentally sent my first reply directly to the OP, and forgot the=20 mailing list - I'm adding it back now, because I don't want the OP to=20 follow my advice until others have confirmed or corrected it!) On 09/05/2012 21:53, Patrik Horn=EDk 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=3Dpre= serve > 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 synchron= ise". Of course, another possibility is that if you have the space in the=20 system for another drive, you may want to convert to a full raid6 for=20 the future. That way you have the extra safety built-in in advance.=20 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= =20 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 RAID= 6 > it should be left-symmetric-6. Is RAID6 working without problem in > degraded mode with this layout, no matter which one or two drives ar= e > missing? > The layout will not affect the redundancy or the features of the raid -= =20 it will only (slightly) affect the speed of some operations. > - What happens in step 5 and how long does it take? (If it is withou= t > 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=20 getting out of my depth here - it all depends on how the disks get=20 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=20 much simpler and faster than these sorts of re-shaping - it's exactly=20 the sort of situation the feature was designed for. But I don't know i= f=20 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=20 wrote: >> On 08/05/12 11:10, Patrik Horn=EDk 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 / reliabili= ty? >>> Do you recommend it on production data? >>> >>> Thanks. >>> >> >> If you don't want to play with the "bleeding edge" features, you=20 could add >> the disk and extend the array to RAID6, then remove the old drive. = I=20 think >> if you want to do it all without doing any re-shapes, however, then= =20 you'd >> need a third drive (the extra drive could easily be an external USB= =20 disk if >> needed - it will only be used for writing, and not for reading unle= ss >> 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=20 layout. Then >> fail and remove the old drive. Put the new drive into the box and=20 add it as >> a hot spare. It should automatically take its place in the raid5,=20 replacing >> the old one. Once it has been rebuilt, you can fail and remove the= =20 extra >> drive, then re-shape back to raid5. >> >> If things go horribly wrong, the external drive gives you your pari= ty >> protection. >> >> Of course, don't follow this plan until others here have commented=20 on it, >> and either corrected or approved it. >> >> And make sure you have a good backup no matter what you decide to d= o. >> >> mvh., >> >> David >> > > -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html