From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from frost.carfax.org.uk ([85.119.82.111]:33583 "EHLO frost.carfax.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756929Ab3GZOpz (ORCPT ); Fri, 26 Jul 2013 10:45:55 -0400 Date: Fri, 26 Jul 2013 15:45:53 +0100 From: Hugo Mills To: Axelle Cc: linux-btrfs@vger.kernel.org Subject: Re: Adding 500G disk to btrfs volume... but I don't get 500G more of available space (raid0) Message-ID: <20130726144553.GL20517@carfax.org.uk> References: <20130726074508.GJ20517@carfax.org.uk> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="umrsQkkrw7viUWFs" In-Reply-To: Sender: linux-btrfs-owner@vger.kernel.org List-ID: --umrsQkkrw7viUWFs Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Fri, Jul 26, 2013 at 04:35:59PM +0200, Axelle wrote: > Hi Hugo, > Thanks for your answer, but I'm afraid I still don't get it. > > >RAID-0 requires at least two devices. > > Well, I have three devices, so that's more than enough isn't it? > Or do you mean I should be adding two devices at a time? > > > If you balance this > >configuration, you'll use up the first 93.13 GiB of each device > >striping across all three devices, for a total of 3*93.13 = 279.39 > > why 93.13? I guess you meant 84.53 which is the size I am using on > sdc1 and sdc6. Sorry, a little unclear -- if you balance, and then continue writing data to the FS. Once you hit 93.13 GiB (the size of the smallest device), you switch to 2-device operation, and then when that's full, you can't go any further. > ># btrfs balance start -dconvert=single,soft /samples > > Nice command but I wasn't thinking of stopping RAID0 striping. I was > expecting my data to be stripped evenly on all 3 devices. It's worth noting that /dev/sdc1 and /dev/sdc6 are on the same physical device. If that's a rotational device (i.e. traditional hard disk), then you're going to have a serious performance decrease as a result of that, because /dev/sdc will have to spend lots of its time seeking between the two partitions. "single" operation really is the better option here -- you'll get to use all your space, and you won't suffer the performance problems of striping between two partitions on the same disk. > Well - evenly - until the smallest one /dev/sdc1 is filled, then, > it'll use only the last two, when /dev/sdc6 is filled, it will used > /dev/sdb only. > Is that possible/correct? That's exactly what happens, except for the last bit. RAID-0 requires at least two devices, so it can't stripe across the one device remaining once you have completely filled /dev/sdc1 and /dev/sdc6. > But basically, what does not make sense to me is what df reports as > available size. > Look. > Before, I had ~165G used on a total of 194G. > I added a new disk of 465G. Now, df reports I have a total of 660G > (that's right) with 165G used (that's correct too) but only 43G > available! > > I was expecting to have ~495G available! Where are my 465G gone? It's not usable with the RAID configuration you've specified, so it's not shown. Hugo. > $ df -h > Filesystem Size Used Avail Use% Mounted on > ... > /dev/sdc1 660G 165G 43G 80% /samples > > > > Thanks > Axelle. > > On Fri, Jul 26, 2013 at 9:45 AM, Hugo Mills wrote: > > On Fri, Jul 26, 2013 at 09:05:03AM +0200, Axelle wrote: > >> Hi btrfs folks, > >> > >> I'm afraid I have a newbie question... but I can't sort it out? It's > >> just about adding a disk to a btrfs volume and not getting the correct > >> amount of GB in the end... > >> > >> I have a btrfs volume which already consists of two different devices > >> and which is mounted on /samples. Its total size is 194G. > >> > >> $ df -h > >> Filesystem Size Used Avail Use% Mounted on ... /dev/sdc1 194G 165G 20G > >> 90% /samples > >> > >> Now, I would like to add another 500G to that volume, from another device. I did > >> > >> $ sudo mkfs.btrfs -m raid0 -d raid0 /dev/sdb > >> $ sudo btrfs device add /dev/sdb /samples > >> My filesystem now correctly reports: > >> > >> $ sudo btrfs filesystem show > >> Label: none uuid: 545e95c6-d347-4a8c-8a49-38b9f9cb9add > >> Total devices 3 FS bytes used 161.98GB > >> devid 3 size 465.76GB used 0.00 path /dev/sdb > >> devid 2 size 93.13GB used 84.51GB path /dev/sdc1 > >> devid 1 size 100.61GB used 84.53GB path /dev/sdc6 > >> But I miss some space when I do: > > > > RAID-0 requires at least two devices. If you balance this > > configuration, you'll use up the first 93.13 GiB of each device > > striping across all three devices, for a total of 3*93.13 = 279.39 > > GiB. Then /dev/sdc1 becomes full, leaving you with two devices which > > have 7.48 GiB and 372.63 GiB respectively. After another 7.48 GiB on > > each device (for a total of 2*7.48 = 14.96 GiB), you have filled > > /dev/sdc1, leaving only /dev/sdb to work with. Since there's only one > > device, it can't be used by RAID-0. > > > > If you want to use the full space available, you should rebalance > > to single usage, which stops the RAID-0 striping, and allocates > > linearly: > > > > # btrfs balance start -dconvert=single,soft /samples > > > > Hugo. > > > >> $ df -h > >> Filesystem Size Used Avail Use% Mounted on > >> ... > >> /dev/sdc1 660G 165G 43G 80% /samples > >> I added 500G! Why haven't I got more available?? > >> > >> To debug, I ran this command: > >> > >> $ sudo btrfs filesystem df /samples > >> Data, RAID0: total=162.00GB, used=159.79GB > >> Data: total=8.00MB, used=7.48MB > >> System, RAID1: total=8.00MB, used=24.00KB > >> System: total=4.00MB, used=0.00 > >> Metadata, RAID1: total=3.50GB, used=2.19GB > >> Metadata: total=8.00MB, used=0.00 > >> My data is in RAID0, that's ok. So where have my 500G gone, and how > >> can I fix this? > >> > >> Thanks > >> -- > >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > >> the body of a message to majordomo@vger.kernel.org > >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > -- > > === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === > > PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk > > --- Sometimes, when I'm alone, I Google myself. --- > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- I hate housework. 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