Axelle
2013-Jul-26 07:05 UTC
Adding 500G disk to btrfs volume... but I don''t get 500G more of available space (raid0)
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:
$ 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
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Hugo Mills
2013-Jul-26 07:45 UTC
Re: Adding 500G disk to btrfs volume... but I don''t get 500G more of available space (raid0)
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. ---
Axelle
2013-Jul-26 14:35 UTC
Re: Adding 500G disk to btrfs volume... but I don''t get 500G more of available space (raid0)
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 = 279.39why 93.13? I guess you meant 84.53 which is the size I am using on sdc1 and sdc6.># btrfs balance start -dconvert=single,soft /samplesNice command but I wasn''t thinking of stopping RAID0 striping. I was expecting my data to be stripped evenly on all 3 devices. 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? 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? $ 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 <hugo@carfax.org.uk> 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
2013-Jul-26 14:45 UTC
Re: Adding 500G disk to btrfs volume... but I don''t get 500G more of available space (raid0)
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 <hugo@carfax.org.uk> 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. You make the beds, you wash the dishes, and --- six months later you have to start all over again.