Hi, I''m starting to play with btrfs on my new computer. I''m running Gentoo and have compiled the 2.6.31 kernel, enabling btrfs. Now I have 2 partitions (on 2 different sata disks) that are free for me to play with, each about 375 gb in size. I wanted to create a "raid1" volume using these two partitions, so I did: # mkfs.btrfs -d raid1 /dev/sda5 /dev/sdb5 # mount /dev/sda5 /btrfs and everything seems fine. Now what I find strange is that everything looks like a raid0 was created, not a raid1: $ df -h /btrfs/ Filesystem Size Used Avail Use% Mounted on /dev/sda5 684G 72G 612G 11% /btrfs What am I doing (or understanding) wrong? Thanks! Jp -- 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
yOn Fri, Nov 27, 2009 at 03:41:17PM -0500, Jean-Philippe Robichaud wrote:> Now I have 2 partitions (on 2 different sata disks) that are free for me to > play with, each about 375 gb in size. I wanted to create a "raid1" volume > using these two partitions, so I did: > > # mkfs.btrfs -d raid1 /dev/sda5 /dev/sdb5 > # mount /dev/sda5 /btrfs > > and everything seems fine. > > Now what I find strange is that everything looks like a raid0 was created, not > a raid1: > > $ df -h /btrfs/ > Filesystem Size Used Avail Use% Mounted on > /dev/sda5 684G 72G 612G 11% /btrfs > > What am I doing (or understanding) wrong?It''s effectively showing you the number of unallocated blocks, so (with a RAID-1, single-redundancy filesystem), files will appear to take twice as much of your free space as you think they should: write a 2GiB file to that filesystem, and free space will drop by 4GiB. I think that the reasoning behind this is that if you''re using per-object mirroring/striping, it''s impossible to give a precise count of the free space remaining on the volume in any meaningful way: write a 1GiB striped file, and you''ll take 1GiB of space; write the same file mirrored, and you''ll take 2GiB of space. Hugo. -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk == PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- There are three mistaiks in this sentance. ---
On Friday 27 November 2009 16:04:42 Hugo Mills wrote:> yOn Fri, Nov 27, 2009 at 03:41:17PM -0500, Jean-Philippe Robichaud wrote: > > Now I have 2 partitions (on 2 different sata disks) that are free for me > > to play with, each about 375 gb in size. I wanted to create a "raid1" > > volume using these two partitions, so I did: > > > > # mkfs.btrfs -d raid1 /dev/sda5 /dev/sdb5 > > # mount /dev/sda5 /btrfs > > > > and everything seems fine. > > > > Now what I find strange is that everything looks like a raid0 was > > created, not a raid1: > > > > $ df -h /btrfs/ > > Filesystem Size Used Avail Use% Mounted on > > /dev/sda5 684G 72G 612G 11% /btrfs > > > > What am I doing (or understanding) wrong? > > It''s effectively showing you the number of unallocated blocks, so > (with a RAID-1, single-redundancy filesystem), files will appear to > take twice as much of your free space as you think they should: write > a 2GiB file to that filesystem, and free space will drop by 4GiB. > > I think that the reasoning behind this is that if you''re using > per-object mirroring/striping, it''s impossible to give a precise count > of the free space remaining on the volume in any meaningful way: write > a 1GiB striped file, and you''ll take 1GiB of space; write the same > file mirrored, and you''ll take 2GiB of space. > > Hugo. >Thanks for your input Hugo, but somehow it looks like something different is happening: du toto 1088 toto $ df . /dev/sda5 716579256 75455900 641123356 11% /btrfs $ cp toto toto2 $ btrfsctl -c . $ df . /dev/sda5 716579256 75456992 641122264 11% /btrfs So 1092 block were ''consumed'', we''re far from the +2000 I would have expected... Is there a place in /sys or /proc where I could perhaps get ''stats'' about the btrfs volume? -- 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
Hello Jean-Philippe, Jean-Philippe Robichaud wrote (ao):> Is there a place in /sys or /proc where I could perhaps get ''stats'' > about the btrfs volume?I think btrfs-show should help you there. With kind regards, Sander -- Humilis IT Services and Solutions http://www.humilis.net -- 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
On Sunday 29 November 2009 07:42:56 Sander wrote:> Hello Jean-Philippe, > > Jean-Philippe Robichaud wrote (ao): > > Is there a place in /sys or /proc where I could perhaps get ''stats'' > > about the btrfs volume? > > I think btrfs-show should help you there. > > With kind regards, Sander >Sure: here it goes: # sudo btrfs-show failed to read /dev/sr0 Label: none uuid: fb9270b4-8779-489f-a599-eaab299d4633 Total devices 2 FS bytes used 78.98GB devid 1 size 341.69GB used 146.03GB path /dev/sda5 devid 2 size 341.69GB used 146.01GB path /dev/sdb5 -- 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
On Sun, Nov 29, 2009 at 4:28 PM, Jean-Philippe Robichaud <jean.philippe.robichaud@gmail.com> wrote:> > On Sunday 29 November 2009 07:42:56 Sander wrote: > > Hello Jean-Philippe, > > > > Jean-Philippe Robichaud wrote (ao): > > > Is there a place in /sys or /proc where I could perhaps get ''stats'' > > > about the btrfs volume? > > > > I think btrfs-show should help you there. > > > > With kind regards, Sander > > > Sure: here it goes: > > # sudo btrfs-show > failed to read /dev/sr0 > > Label: none uuid: fb9270b4-8779-489f-a599-eaab299d4633 > Total devices 2 FS bytes used 78.98GB > devid 1 size 341.69GB used 146.03GB path /dev/sda5 > devid 2 size 341.69GB used 146.01GB path /dev/sdb5 >I''m not sure I actually understand how to read this.The size of each device make sense (341GB) as it is the size of both partitions. Now the FS-bytes-used also make sense as it is about the size of data that I''ve copied, but the per-device used space seems strange to me and the output of "df -h" is also hard to interpret: Filesystem Size Used Avail Use% Mounted on /dev/sda5 684G 79G 605G 12% /btrfs I would have understood if the "Used" field would have been 160GB or if "Avail" would have dropped to 520GB. I guess that I''ll come to a point where Used will be 340GB and Avail will also be 340GB but I''ll be getting No Space Left On Device errors? -- 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