Re: [raidX vs single/dup]
On Thu, Sep 26, 2013 at 12:22:49PM +, miaou sami wrote: Hi btrfs guys, could someone explain to me the differences in mkfs.btrfs: - between -d raid0 and -d single In RAID0, data is striped across all the devices, so the first 64k of a file will go on device 1, the next 64k will go on device 2, and so on. With single, files are allocated linearly on one device. (This is assuming smallish files, a filesystem with lots of space. Even with single, files can still end up being scattered around over multiple devices -- but with RAID0, even non-fragmented files are striped) - between -m raid1 and -m dup In both cases, there are two copies of each metadata block. With RAID1, it *requires* the two copies to live on different devices. With DUP, it allows the two copies to live on the same device (e.g. if there's only one device). - between -m raid0 and -m single As for -draid0 and -dsingle, but for metadata instead of data. My understanding is that raidX should be used in case of multi devices and single/dup should be used in case of single device to allow duplication, but it is not 100% clear to me... As btrfs raid concepts are quite different from traditionnal raid, shouldn't we use the words stripped and mirrored instead of raid0/raid1? or even single and duplicated? Then there would be no difference between single/raid0 and duplicated/raid1... But there _are_ differences between them, as explained above. :) I posted a patch a while ago to change the names to something more logical and expressive, but it didn't get merged. Hugo. -- === 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 --- Stick them with the pointy end. --- signature.asc Description: Digital signature
RE: [raidX vs single/dup]
Thank you, it is quite clear now. I guess that on multi device, raid0 vs single would be a matter of performance vs ease of low level hardware data recovery. The wiki https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices says: When you have drives with differing sizes and want to use the full capacity of each drive, you have to use the single profile for the data blocks. Let's assume the following configuration: 1x10GB disk and 2x5GB disks -- Does it mean I cannot use the full capacity AND have a duplication of my data in the configuration above? (full capacity would be 10GB here) -- If I try to setup either -d raid1 or -d dup on that configuration, what will I get? -- Is there any behavior difference between raid1 / dup in that case? -- Can raid1 ensure that data are always duplicated on different devices AND take advantage of all available space? Regards, Sam Date: Thu, 26 Sep 2013 13:32:33 +0100 From: h...@carfax.org.uk To: miaous...@hotmail.com CC: linux-btrfs@vger.kernel.org Subject: Re: [raidX vs single/dup] On Thu, Sep 26, 2013 at 12:22:49PM +, miaou sami wrote: Hi btrfs guys, could someone explain to me the differences in mkfs.btrfs: - between -d raid0 and -d single In RAID0, data is striped across all the devices, so the first 64k of a file will go on device 1, the next 64k will go on device 2, and so on. With single, files are allocated linearly on one device. (This is assuming smallish files, a filesystem with lots of space. Even with single, files can still end up being scattered around over multiple devices -- but with RAID0, even non-fragmented files are striped) - between -m raid1 and -m dup In both cases, there are two copies of each metadata block. With RAID1, it *requires* the two copies to live on different devices. With DUP, it allows the two copies to live on the same device (e.g. if there's only one device). - between -m raid0 and -m single As for -draid0 and -dsingle, but for metadata instead of data. My understanding is that raidX should be used in case of multi devices and single/dup should be used in case of single device to allow duplication, but it is not 100% clear to me... As btrfs raid concepts are quite different from traditionnal raid, shouldn't we use the words stripped and mirrored instead of raid0/raid1? or even single and duplicated? Then there would be no difference between single/raid0 and duplicated/raid1... But there _are_ differences between them, as explained above. :) I posted a patch a while ago to change the names to something more logical and expressive, but it didn't get merged. Hugo. -- === 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 --- Stick them with the pointy end. --- -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [raidX vs single/dup]
On Thu, Sep 26, 2013 at 01:40:57PM +, miaou sami wrote: Thank you, it is quite clear now. I guess that on multi device, raid0 vs single would be a matter of performance vs ease of low level hardware data recovery. The wiki https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices says: When you have drives with differing sizes and want to use the full capacity of each drive, you have to use the single profile for the data blocks. Let's assume the following configuration: 1x10GB disk and 2x5GB disks -- Does it mean I cannot use the full capacity AND have a duplication of my data in the configuration above? (full capacity would be 10GB here) No, that will give you the full usable space. A 20 GB drive and two 5 GB drives would not, though. -- If I try to setup either -d raid1 or -d dup on that configuration, what will I get? Try it for yourself in the space simulator: http://carfax.org.uk/btrfs-usage/ -- Is there any behavior difference between raid1 / dup in that case? If you have multiple disks, I think DUP gets automatically upgraded to RAID-1 (i.e. the different copies on different devices requirement is enforced). So, no. -- Can raid1 ensure that data are always duplicated on different devices AND take advantage of all available space? Depends on the relative sizes of the devices. If your largest device is bigger than the rest put together, then you'll lose some space. Hugo. Regards, Sam Date: Thu, 26 Sep 2013 13:32:33 +0100 From: h...@carfax.org.uk To: miaous...@hotmail.com CC: linux-btrfs@vger.kernel.org Subject: Re: [raidX vs single/dup] On Thu, Sep 26, 2013 at 12:22:49PM +, miaou sami wrote: Hi btrfs guys, could someone explain to me the differences in mkfs.btrfs: - between -d raid0 and -d single In RAID0, data is striped across all the devices, so the first 64k of a file will go on device 1, the next 64k will go on device 2, and so on. With single, files are allocated linearly on one device. (This is assuming smallish files, a filesystem with lots of space. Even with single, files can still end up being scattered around over multiple devices -- but with RAID0, even non-fragmented files are striped) - between -m raid1 and -m dup In both cases, there are two copies of each metadata block. With RAID1, it *requires* the two copies to live on different devices. With DUP, it allows the two copies to live on the same device (e.g. if there's only one device). - between -m raid0 and -m single As for -draid0 and -dsingle, but for metadata instead of data. My understanding is that raidX should be used in case of multi devices and single/dup should be used in case of single device to allow duplication, but it is not 100% clear to me... As btrfs raid concepts are quite different from traditionnal raid, shouldn't we use the words stripped and mirrored instead of raid0/raid1? or even single and duplicated? Then there would be no difference between single/raid0 and duplicated/raid1... But there _are_ differences between them, as explained above. :) I posted a patch a while ago to change the names to something more logical and expressive, but it didn't get merged. Hugo. -- === 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 --- Nothing right in my left brain. Nothing left in --- my right brain. signature.asc Description: Digital signature
Re: [raidX vs single/dup]
On Thu, Sep 26, 2013 at 02:55:38PM +, miaou sami wrote: OK, that's clear. Nice space simulator btw :-) you should add a link somewhere in btrfs wiki... There is one, linked from the first line of the relevant section in the FAQ. Hugo. Thanks Date: Thu, 26 Sep 2013 14:46:05 +0100 From: h...@carfax.org.uk To: miaous...@hotmail.com CC: linux-btrfs@vger.kernel.org Subject: Re: [raidX vs single/dup] On Thu, Sep 26, 2013 at 01:40:57PM +, miaou sami wrote: Thank you, it is quite clear now. I guess that on multi device, raid0 vs single would be a matter of performance vs ease of low level hardware data recovery. The wiki https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices says: When you have drives with differing sizes and want to use the full capacity of each drive, you have to use the single profile for the data blocks. Let's assume the following configuration: 1x10GB disk and 2x5GB disks -- Does it mean I cannot use the full capacity AND have a duplication of my data in the configuration above? (full capacity would be 10GB here) No, that will give you the full usable space. A 20 GB drive and two 5 GB drives would not, though. -- If I try to setup either -d raid1 or -d dup on that configuration, what will I get? Try it for yourself in the space simulator: http://carfax.org.uk/btrfs-usage/ -- Is there any behavior difference between raid1 / dup in that case? If you have multiple disks, I think DUP gets automatically upgraded to RAID-1 (i.e. the different copies on different devices requirement is enforced). So, no. -- Can raid1 ensure that data are always duplicated on different devices AND take advantage of all available space? Depends on the relative sizes of the devices. If your largest device is bigger than the rest put together, then you'll lose some space. Hugo. Regards, Sam Date: Thu, 26 Sep 2013 13:32:33 +0100 From: h...@carfax.org.uk To: miaous...@hotmail.com CC: linux-btrfs@vger.kernel.org Subject: Re: [raidX vs single/dup] On Thu, Sep 26, 2013 at 12:22:49PM +, miaou sami wrote: Hi btrfs guys, could someone explain to me the differences in mkfs.btrfs: - between -d raid0 and -d single In RAID0, data is striped across all the devices, so the first 64k of a file will go on device 1, the next 64k will go on device 2, and so on. With single, files are allocated linearly on one device. (This is assuming smallish files, a filesystem with lots of space. Even with single, files can still end up being scattered around over multiple devices -- but with RAID0, even non-fragmented files are striped) - between -m raid1 and -m dup In both cases, there are two copies of each metadata block. With RAID1, it *requires* the two copies to live on different devices. With DUP, it allows the two copies to live on the same device (e.g. if there's only one device). - between -m raid0 and -m single As for -draid0 and -dsingle, but for metadata instead of data. My understanding is that raidX should be used in case of multi devices and single/dup should be used in case of single device to allow duplication, but it is not 100% clear to me... As btrfs raid concepts are quite different from traditionnal raid, shouldn't we use the words stripped and mirrored instead of raid0/raid1? or even single and duplicated? Then there would be no difference between single/raid0 and duplicated/raid1... But there _are_ differences between them, as explained above. :) I posted a patch a while ago to change the names to something more logical and expressive, but it didn't get merged. Hugo. -- === 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 --- The trouble with you, Ibid, is you think you know everything. --- signature.asc Description: Digital signature
RE: [raidX vs single/dup]
OK, that's clear. Nice space simulator btw :-) you should add a link somewhere in btrfs wiki... Thanks Date: Thu, 26 Sep 2013 14:46:05 +0100 From: h...@carfax.org.uk To: miaous...@hotmail.com CC: linux-btrfs@vger.kernel.org Subject: Re: [raidX vs single/dup] On Thu, Sep 26, 2013 at 01:40:57PM +, miaou sami wrote: Thank you, it is quite clear now. I guess that on multi device, raid0 vs single would be a matter of performance vs ease of low level hardware data recovery. The wiki https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices says: When you have drives with differing sizes and want to use the full capacity of each drive, you have to use the single profile for the data blocks. Let's assume the following configuration: 1x10GB disk and 2x5GB disks -- Does it mean I cannot use the full capacity AND have a duplication of my data in the configuration above? (full capacity would be 10GB here) No, that will give you the full usable space. A 20 GB drive and two 5 GB drives would not, though. -- If I try to setup either -d raid1 or -d dup on that configuration, what will I get? Try it for yourself in the space simulator: http://carfax.org.uk/btrfs-usage/ -- Is there any behavior difference between raid1 / dup in that case? If you have multiple disks, I think DUP gets automatically upgraded to RAID-1 (i.e. the different copies on different devices requirement is enforced). So, no. -- Can raid1 ensure that data are always duplicated on different devices AND take advantage of all available space? Depends on the relative sizes of the devices. If your largest device is bigger than the rest put together, then you'll lose some space. Hugo. Regards, Sam Date: Thu, 26 Sep 2013 13:32:33 +0100 From: h...@carfax.org.uk To: miaous...@hotmail.com CC: linux-btrfs@vger.kernel.org Subject: Re: [raidX vs single/dup] On Thu, Sep 26, 2013 at 12:22:49PM +, miaou sami wrote: Hi btrfs guys, could someone explain to me the differences in mkfs.btrfs: - between -d raid0 and -d single In RAID0, data is striped across all the devices, so the first 64k of a file will go on device 1, the next 64k will go on device 2, and so on. With single, files are allocated linearly on one device. (This is assuming smallish files, a filesystem with lots of space. Even with single, files can still end up being scattered around over multiple devices -- but with RAID0, even non-fragmented files are striped) - between -m raid1 and -m dup In both cases, there are two copies of each metadata block. With RAID1, it *requires* the two copies to live on different devices. With DUP, it allows the two copies to live on the same device (e.g. if there's only one device). - between -m raid0 and -m single As for -draid0 and -dsingle, but for metadata instead of data. My understanding is that raidX should be used in case of multi devices and single/dup should be used in case of single device to allow duplication, but it is not 100% clear to me... As btrfs raid concepts are quite different from traditionnal raid, shouldn't we use the words stripped and mirrored instead of raid0/raid1? or even single and duplicated? Then there would be no difference between single/raid0 and duplicated/raid1... But there _are_ differences between them, as explained above. :) I posted a patch a while ago to change the names to something more logical and expressive, but it didn't get merged. Hugo. -- === 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 --- Nothing right in my left brain. Nothing left in --- my right brain. -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
