From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: Linear device of two arrays Date: Mon, 10 Jul 2017 08:37:52 +1000 Message-ID: <87van15j9b.fsf@notabene.neil.brown.name> References: <20170705214250.0ea99538@natsu> <595D2ADA.8010907@youngman.org.uk> <5afd5cea-06b8-8524-e4f5-8534f23bd714@hardwarefreak.org> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha256; protocol="application/pgp-signature" Return-path: In-Reply-To: <5afd5cea-06b8-8524-e4f5-8534f23bd714@hardwarefreak.org> Sender: linux-raid-owner@vger.kernel.org To: Stan Hoeppner , veljko3@gmail.com, linux-raid@vger.kernel.org List-Id: linux-raid.ids --=-=-= Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On Sat, Jul 08 2017, Stan Hoeppner wrote: > On 07/08/2017 05:26 AM, Veljko wrote: >> On Sat, Jul 8, 2017 at 12:52 AM, Stan Hoeppner = wrote: >>> On 07/07/2017 03:26 PM, Veljko wrote: >>>> I just noticed that I replied to Wol insted to list. >>>> >>>> On Wed, Jul 5, 2017 at 8:07 PM, Wols Lists >>>> wrote: >>>>> On 05/07/17 17:42, Roman Mamedov wrote: >>>>>> On Wed, 5 Jul 2017 17:34:09 +0200 >>>>>> Veljko wrote: >>>>>> >>>>>>> Hello, >>>>>>> >>>>>>> I have a RAID10 device which I have formated using the mkfs.xfs >>>>>>> defaults (Stan helped me with this few years back). I reached 88% >>>>>>> capacity and it is time to expand it. I bought 4 more drives to cre= ate >>>>>>> another RIAD10 array. I would like to create linear device out of >>>>>>> those two and grow XFS across the 2nd device. How can this be done >>>>>>> without loosing the existing device's data? I would also like to ad= d a >>>>>>> spare HDD. Do I have to have a separate spare HDD for each array or >>>>>>> one can be used by both of them? >>>>>> Why make another RAID10? With modern versions of mdadm and kernel you >>>>>> should >>>>>> be able to simply reshape the current RAID10 to increase the number = of >>>>>> devices used from 4 to 8. >>>>>> >>>>>> >>>>> I was thinking of replying, but isn't that not possible for some >>>>> versions of RAID-10? >>>>> >>>>> My feeling was, if you can't just add drives to the existing raid 10, >>>>> create a new one which you can expand, migrate the fs across (btrfs >>>>> would let you do that live, I believe, so xfs probably can too), then >>>>> you can scrap the old raid-10 and add the drives into the new one. >>>>> >>>>> Cheers, >>>>> Wol >>>> >>>> Thanks for your input, Roman and Wol. >>>> >>>> Expanding existing RAID is one of the options, but I was advised by >>>> Stan Hoeppner to do it this way and I tend to believe him on this >>>> subject. With my metadata heavy backup workload, this will provide >>>> better performance. >>>> >>>> So my question is still, how can an existing array be added to linear >>>> device, and it's file system expanded over the second array. >>> For this to work the existing RAID10 array must already be a member of a >>> linear device with one component device. If this linear array already >>> exists then you could add another RAID10 array to the linear device. I= f you >>> currently have an XFS filesystem sitting atop a 'bare' RAID10 then I do= n't >>> believe the linear option will work for you. Thus I'd tend to agree wi= th >>> others that reshaping your current RAID10 is the best option. >>> >>> My apologies if I wasn't clear in my previous advice. >>> >>> Stan >> Here is your previous advice: >> "Do not use LVM. Directly format the RAID10 device using the mkfs.xfs >> defaults. mkfs.xfs will read the md configuration and automatically >> align the filesystem to the stripe width. >> >> When the filesystem reaches 85% capacity, add 4 more drives and create >> another RAID10 array. At that point we'll teach you how to create a >> linear device of the two arrays and grow XFS across the 2nd array." >> >> From this I concluded that it is possible to create linear device >> using existing array, but since it is not the case, I'll just have to >> create new array, move data to it, than add first array to a new >> linear device (1 member), copy my data to it, and than join second >> device to it. I wanted to avoid all this copying but will have to do >> it. Than I will add one drive to spare-group both arrays will be a >> members of, as advised by Andreas. Does this sound OK? > > Yes. Although, I was hoping Neil Brown would chime in here. I'm not=20 > entirely sure that you can't do this the way I originally mentioned. I wasn't clear to me that I needed to chime in.. and the complete lack of details (not even an "mdadm --examine" output), meant I could only answer in vague generalizations. However, seeing you asked. If you really want to have a 'linear' of 2 RAID10s, then 0/ unmount the xfs filesystem 1/ backup the last few megabytes of the device dd if=3D/dev/mdXX of=3D/safe/place/backup bs=3D1M skip=3D$BIGNUM 2/ create a linear array of the two RAID10s, ensuring the metadata is v1.0, and the dataoffset is zero (should be default with 1.0) mdadm -C /dev/mdZZ -l linear -n 2 -e 1.0 --data-offset=3D0 /dev/mdXX /d= ev/mdYY 3/ restore the saved data dd of=3D/dev/mdZZ if=3D/safe/place/backup bs=3D1M seek=3D$BIGNUM 4/ grow the xfs filesystem 5/ be happy. I cannot comment on the values of "few" and "$BUGNUM" without seeing specifics. 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